Thanks for all the replies everyone.
I'll try my brothers Antec Earthwatts PSU sometime soon, but it means taking apart both rigs, and that's time consuming. I'm going to work shortly, but might have time to do it this evening. Otherwise it'll be waiting til Wednesday. It's killing me not having my PC!!
If it is the PSU, I expect I'll take the plunge and get myself a fancy Corsair one. Even though it really pains me to spend SO much money on a PSU. If it turns out the PSU doesn't make a difference when I try my brothers one, I'll try the motherboard out of his as well. Either way, I'm going to be buying two things minimum:
1. A Corsair power supply. I figure it's an investment to help protect my PC, and, being a fancy Corsair one, I should gain at least 2 extra e-inches.
2. A surge protector!!