Are you sure the PSU and HDD are not faulty? Might be the cause of some of your problems... Especially I'd be wary of the PSU, suppose it gives some nice power spikes to the rest of the hardware? You could check the SMART data from the HDD to see if it causes any of the problems.
I agree that 2GB is not much for a gaming system, I forgot to multiply it by 2.
What's wrong with the PSU? The problems I got was the fault of a broken GPU, but the problem I now have is that everything freezes so I can't do a thing. Sometimes it even freezes before i get to see the Gigabytescreen (it's a Gigabyte mobo).