If it's a power issue, it's unlikely to be the motherboard, more likely the Power supply unit at the top.

It could be possible that you've got too many devices needing power from it, so it can't cope (lke lots of HDs/CDRW/DVDs, lots of fans, and a beefy GFX card). Is it one of those low 200W-250W supplys, or a better 300W or even 400W ones?