Originally Posted by
~aoe~
I recently had a strange problem with another motherboard. Whilst not the same problem, it was sort of similar.
After changing the CPU and chipset heatsinks on my 2nd system (Opteron 170 on A8N32-SLi), I tried to increase my OC by upping the voltages. I wasn't able to get the system stable, so dropped back to the previous OC. However, after these changes, the PC was unable to fully switch off. Windows would fully close down, but the fans would just keep spinning until I switched off the PSU. The same problem occurred when trying to Restart (would hang in BIOS with all fans spinning).
After trying to increase the OC again, I had a boot failure that reset the BIOS to defaults. After this, the problem disappeared. Even after reapplying the OC settings in BIOS, the problem was gone.
Long story, but I think it was something in BIOS that was causing this problem, and by resetting to defaults, it seems to have fixed it. May be worth trying.