I would re-do the cabling, re-seat the hardware like memory modules, something could be out of place not providing enought eletrical contact. The PSU could be a factor however the probabilities lie with the board.
Try resetting BIOS to defaults or CMOS clear and change the battery too, could be old enough.
If all fails, either you go for a used cheap AM3+ board, with some luck maybe you'll grab something under 20.
Good luck
The Englishman