If I Have A Fan Fail Will My PC Detect it and shut down

if your PC was newer, it most likely will shut down if it feels the CPU starting to execute some errors due the heat stress. And IIRC, all CPU's these days incorporate a Temp Lead into the core. Also, some chipsets will monitor the temp inside them too. You would have to enter your BIOS to see. If you see any temp ratings (CPU, Chipset, PSU, etc...) then you most likely have one that does.
These days, heat consideration is taken into account of preventative measures that companies do to prevent a crap load of them coming into them with core melt-downs and other stuff.

Myself, my PC will restart 2x if the CPU grinds to a halt from heat, the third time, it shuts the PC off entirely. Believe me, in my old room, I was hitting those temps quite often, and would have to drag my PC to the diningroom table in the summer (mom was not too happy about that, but the situation has been resolved ) to do some serious computing.

if you have any computer built within the last 3 yrs, then it is safe to say that it has some heat guard built into it.

also, if you are worried, put in an extra fan or two. Chances are, all of them won't fail at the same time, so check your fans often. I just had to replace my chipset fan, b/c it won't move at all, but not to worry, I have about 7 other fans in there as well, so it constantly has a fresh air flow.

Thanks for the help!

Modern PCs have thermal limits, in the case of even newer machines, thermal throttling. Athlon 64's and newer Pentium 4's will throttle down their core speed to keep from overheating. You can technically run them without heatsinks, but at very poor speeds. Intel calls this Speedstep, AMD calls their's Cool'n'Quiet.

For older ones, at least Athlons then up (P4's for that matter), have sensors and thermal limits. Currently, if my core goes above 70C, the machine will halt. Also, some BIOS will detect if a fan's RPM goes from it's normal speed to zero, and either sound of an alarm (internal speaker), or halt.

In older machines, this is hit and miss. But generally, older boxes don't generate *that* much heat under normal loads, but under high loads and things could get unstable. But generally, fans last a LONG time. I'm using some 10 year old ones in this PC (which is one of the reasons why it cost only 330USD to build myself), they function fine.

Fans will generally far outlast a PC, but they do need some maintenance from time-to-time.

Quite often (especially if you live in a dry climate or have pets in the house), fans get clogged with dust and debris. The best solution I've found for this is to take the fan out of the machine, secure it in a portable vice (Black & Decker's Workmate is what I use) and turn the leaf blower on it for 30-60s. You definitely want to have the fans off, out and away from the PC when you do this, as that much air can damage a computer. Be sure to go at it from both sides for at least 15s each. You really want to get that unit spinning. Take the fan out of the vice and tap it gently to get the debris out.

I do this approx every 3 months, and I notice a 3-5C drop in case temperature after cleaning the fans and the rest of the dust that accumulates in the rig. Mind you, I also run my machine 24/7/365, YMMV.

Cheers,

The Czar