Gigabyte m720 wont boot up

[petrarca_t]

I have Gigabyte GA-M720-US3 (latest BIOS), Athlon II X2 550 cpu, 3 times hard drives all WD(160 gig, 1TB, and 500 gig).....half the time the system won't boot up to the bios screen then other times goes to post then to the windows 7 password logon and is totally fine.....co incidentally last week the bios would not activate the keyboard and the mouse in the initial stages of booting up.....i reset the bios and that issue was resoloved...but now it refuses to bootup or hangs at the post screen half the time.......the system is not overclocked and running at standard settings......i have only used one stick of 2 gig ram ddr2 800 mem....opposed to the usual 4 gig.....and the same result, the bios has been reset once again; and have also tried booting up with only the c drive and nothing else connected and the same result........any assistance would be appreciated

 

[r_manic]

Power supply issue? Mind posting using multiple lines next time? That will make your question so much easier to understand.