Compatable gigabyte ga 81915pm motherboard

you may not have to format
you should be okay
are you sure power supply is not going
remove cd drive and boot see if you can get to safemode
Are you sure you have'nt had pc opened and maybe loosened a memory
I still don't think it's the motherboard.I would go more for a memory or power supply problem
let me know

my computer usb not working pls help me

I had a problem similar to this with my old Gigabyte motherboard. What happened, was that somehow, the motherboard's hard drive mounting points were corrupting.
I was able to solve this issue by changing where the hard drives were plugged into the motherboard. It's merely a bandaid solution and may not solve the problem permanently, as I had the problem occur about 3 times.

I would suggest removing one drive (hard drive, CD drive, etc.) at a time to see if it will boot the BIOS when the drive is unplugged. If this does not work, I would think that the motherboard may be dead.

I think you can try all LGA775 MB.
BTW, it worked before? or you changed anything?
Maybe you can try other memories.