Interesting issue I encountered with this board - first the original spec
GA-M68M-S2P r1.0 w/ f1 bios
X2 5600+ 2.9G
2 x 1Gb DDR2-667
1 x 400G SATA
1 x DVDRW
CM Centurion 5
Win7 Pro 32bit
Was spot-on until I swapped out the HD 4670 for an HD 5670 (I know not much of an upgrade - just had it laying around lol). There now was a considerably longer delay before the system would POST (literally 3x or 4x the normal time) and playing games caused the system to hard-lock (either one of these would occur - screen frozen / white screen / black screen, only a reset or power cycle was the only resolve).
I swapped out the PSU for an EA-430 (despite the fact the EA-380 could easily handle it no sweat), same problem with lockups when playing any type of demanding game, and even after a full system teardown / inspection / rebuild.
Was about to try another HDD and reinstall Win7 Pro 32b, when I decided to check the BIOS firmware version and noticed it was F1. Grabbed the F5 version, put it on a USB and ran QFLASH - which I have to comment on this - the QFLASH utility is bloody awesome, not having to set up a bootable USB... All I can say is many cheers for this and kudos to Gigabyte. Ok so where was I - ah yes, boot into QFLASH, backup the original F1 to the USB, flash the F5 version - problem solved. The system POST runs really quick (once again), the system has no problem any longer under taxing games.
All I can think of is some type of PCI-E compatibility the F5 provided, and the F1 could not handle well. Just wanted to put this out there and share in case anyone else has encountered a similar issue - I searched extensively, it could be my google-fu-mojo is on permanent holiday