Ibook only works after I hit it

There are similar issues with G3 iBooks and G4 iBooks, be sure the fixes you try are for the G4. The boards have different layouts and chip positions. The GPU is on diffent sides of the logic board.

you've got a late 2004 12" iBook G4 - that'll be a 1.2ghz most likely. Your GPU is on the topside of the board (this is the case with all iBook G4's). Chances are good that you'll need to do a fair amount of surgery.

Things to check in this scenario
1) logic board screws - chances are that they've worked themselves loose prior to this, but the bump was enough to break them loose around inside the computer. - to check these, remove the bottom case and bottom emi shield. Access to the bottom of the logic board is easy.

2) heatsink - video chip issue - this is an issue that is more prevalent on iBook G3's than the iBook G4's. I've seen all of maybe 3-5 machines where putting a shim on the video chip helped. It's a good idea to remove the heatsink and reseat it. You'll need a 5/32 nut driver (can be found at Home Depot as part of a precision tool kit made by General that sells for around $16 - has every other tool you'll ever need for iBook and PowerBook repair) To get to the heatsink, remove the keyboard, airport card, top case, upper emi shield (it's a good idea to have the bottom case off before you start on this).

3) Unless you are getting a solid grey screen on boot, I seriously doubt that your hard drive is where the issue is. Typically when a hard drive goes and prevents the machine from booting, you'll get a solid grey screen. The method I use to determine if the grey screen is from video or an issue in the ATA bus is by going into open firmware (apple, option, o, f on power up). If the machine can go into open firmware, that rules out an issue on the video system as it is now displaying something.

This is my preliminary with limited info. If I may ask, what side was the machine impacted on? (display half or bottom half?) And when you hit it to get it going - where are you hitting it? If you're hitting the display, this may be something as simple as replacing the reed switch/inverter cable. To verify if that's the issue, disconnect this cable (it connects to the logic board just above the fan on the bottom side of the logic board), hook the computer up to an external display and fire it up. Often times, when this $10 part fails, it will give the appearance of a catastrophic failure. (the failure path is typically due to a short in the cable)

Hope this helps. I've seen too many iBook G4's, and taken too many apart. If there's anything more I can do, let me know.

Thanks a lot for all this information.
Yes, it's a 1.2 Ghz.
The computer got hit on the bottom half and it's the same side I hit it on when I try to start it up.
I have no experience of electronics and am a little scared by the idea of opening the computer, but it might be the only option if I don't want to spend the money they asked for the logic board replacement.
I was able to enter the open firmware, but again, only after I hit it to start it up.
For a couple of times, after I reset the nvram, the computer seemed to work fine but after a while it turned off again, this time by showing a few vertical lines of different colors for a few moments.
The headscratcher is that sometimes the screen goes dark blue - just like right before the screensaver comes in - sometimes it goes black like it was off, but I can still hear the hard disk.
Most of the times, when it doesn't startup, the fans start rolling extremely fast.
The thing that upsets me the most is that when it does startup everything works fine, sometimes for hours, which makes me think that the problem might be a loose cable or a screw.
One more thing, I was able to verify the hard disk with the disk utility and it says that it needs repair.
Thanks a lot again.
Hope to hear soon.

Does it not start at all, or does it just not show anything on the screen? It could be that a solder point broke around the battery?

It starts up, even when I don't hit it. Sometimes the fans start rolling like crazy and sometimes they don't, I can hear the Hard Disk though.
It hasn't happened yet that it hasn't started up at all.

If you've never cracked open a laptop before, or aren't comfortable cracking open your iBook, I would recommend having it looked at by an independant Apple Service Provider. If there is a mom and pop type shop in your area that is Apple Authorized, take it there. Though, make sure that they have a portable certified technician on staff so that your computer can be handled on site. Unfortunately, the Apple store and Applecare tech support line are going to be very limited in the level of assistance that can be provided. (without being able to crack it open and begin troubleshooting they won't be able to give you a 100% accurate diagnosis)

Chances are that you will have to pay a bench fee of some kind to have it checked out - this ranges anywhere from $40-$80 at most repair centers and is often waived if you give the go ahead for a repair.

Also, when you state that the issue began after an impact, it becomes classified as "Accidental Damage/Abuse" by Apple, which is a category that is not covered by Applecare or the limited warranty. Depending on how hard the impact was, there may be structrual damage - a cracked frame may also be responsible for similar symptoms.

There is something new about this:
If I put pressure on the bottom of the ibook at the left of the trackpad the computer works fine.
I tried to give it a few small hits in the same point after it starts up, and it turns off showing some color bars.
I read on this forum something about placing something between the GPU and the heatsink, to put pressure on the heatsink?
Does anybody know anything about this?
Thanks

I wrote a whole thing, thinking that this was a G3 you had. Just head to eBay and find a new board.

I just discovered this thread - I have an 800Mhz 12" iBook G4 which has the same issue - it won't boot, I just get a black screen and the fans start up full throttle, no chime, can't start from CD, can't boot into OF. Sometimes I can power down by holding the power button, other times I need to pull the power cable or the battery out.

One time in 20 it will start up, but sometimes I have to hit the left side of the computer rather hard - and hey presto, it will boot.

The computer will occassionally go dark right in the middle of something, but I can usually restart it by holding down the power button. The machine no longer wakes from sleep, so if I keep it on permanently and don't restart or shut down it's ok.

So is this the graphics card/heatsink issue? What actually is the problem? Assuming I have the necessary screwdrivers and tools (I can go and buy them!), can I open the machine and have a go at fixing it myself? The inspection fee at my local authorised Apple reseller is expensive.

Cheers,

Adam

both of your logic boards are faulty. Sticking in shims and the like is a hack that might work, but I wouldn't expect reliability even after you fit them in.

The inspection fee at the repair centers is useless. They have seen loads of iBook G3s and even G4s, and they'll just quote you on a replacement logic board.

If you can't afford that it's because Apple charges a ludicrous price for replacement parts.

As quoted earlier, see if you can find one secondhand, or consider this: someone out there in the world (or at least your country) may be selling their entire, working computer --iBook or similar-- for less than what Apple charges for out-of-warranty parts + labor.

I have an ibook G4 800 12" with exactly the same problems as AdamM.

After a bit of experimenting I have a theory and it is all to do with heat.

-It seems as the ibook gets hotter then the chance of the blank screen occuring gets greater.

-The ibook will then not restart until it has cooled (can be several hours).

-The longer the ibook has been left to cool the longer it will survive at the next startup.

I've tried placing the ibook directly beneath a very cold aircon unit and recovery time seems to be quicker. It isn't due to faulty temperature sensors as these give normal readings (I've checked using some temperature monitoring apps for OS X). My theory is that as something inside the ibook G4 is heating up and expanding it causes the failure. My hunch is that the heatsink is involved.

The ibook G3 workaround was very easy - I put spacers underneath the metal inner casing and it turned from unusuable to totally reliable, however, the G3 fault was due to the GPU coming loose due to bad soldering. Hence the G3 problem was worsened by shaking the laptop. The ibook G4 fault seems to be different as shaking the laptop makes no difference to whether it will fail or not. Can anyone living in cold areas test my theory further by taking it outside?

Does anyone know of a workaround like the G3 solution which works?

Hello I have the same problem as before.
Actually my ibook 2 weeks ago didn't start up showing a gray screen
with a folder lighting in the middle. I was ready to replace the harddrive but suddently today It didnt start up at all but having just the fan spinning like crazy and impossible to stop!
Does any of you guys solved/have news about this problem?
Does apple provide any assistence( extended warranty) fot this problem?

Thank you in advance

Nicola