Canon MP F50 problem

My Canon MP F50 displays "wrong cartridge" & the alarm keeps flashing.
I have tried:
1.replaced w/new cartridges
2.manually cleaned (won't self clean w/alarm flashing)
3.re-positioned cartridges
4.re-aligned printhead

It worked great last time used. (3 days prior)
Turned it on, in the condition it is now in.....
Nothing touched it in between.
Where can you buy parts? exp: printhead or logic board ect.

Please help. It's only 4 yrs. old/mint condition! thanx so much!