My computer have problem detecting my hard drives. When i reboot, it says "Operating system not found". I reboot again and then it work after the fifth time.

Sometime, my comp detect C: but not D:. Something D: but not C:.
Most of the time it doesnt detect anything.

its not just a booting problem, sometime I on my comp and everything crash. I then proceed to reboot and have to try over and over again to reach windows.

I is not a virus problem, i reformated everything.
My fans cannot be dusty.

What would be the problem, is there a solution?

Either your cables connecting the motherboard to the hard drive are faulty OR your hard drive is slowly but surely breaking...

Welcome to PCHF!

IDE cables, faulty hard drive, BIOS update, CMOS reset or jumpers were incorrectly set.

One of the above would have been the cause/fix of this problem.
Marked as Answered.