I've recently upgraded my system and i am getting a new PSU and GPU this friday. But what i have so far is:
MB: Gigabyte GA-MA790FXT-UD5P, Socket-AM3
CPU: AMD Phenom II X4 955 Black Edition
RAM: Corsair Dominator DDR3 1600MHz 4GB CL9
+a nvidia 7600 GS + some crappy PSU called Q-tec at 450W
Now since installing windows xp i've noticed some weird stuff happening when it's been off for the night. After 2-3 minutes it locks up/slows down. Can't really decide since even if the pointer doesn't move i can open the start menu and stuff like that. I always ends up doing a hard reboot and the problem usually persists for 2-4 reboots. Then everything is fine.
Now what i'm wondering is if it could have something to do with the PSU. I have to leave for school in a sec but i'll be back in a couple of hours. So if you need some additional info i'll provide it when i get back.
It could be. If the crappy PSU is providing poor voltages (noisy or out-of-spec), you could get all kinds of problems that will cause lockups. If this is the case, stop using it until your new PSU arrives, as it could be damaging your system.
Faulty memory is also a possibility. Test each stick individually. If you find one stick that works, test it in each of your RAM slots to rule out a defective slot. Is the voltage for it set right in the BIOS? If each stick works by itself, but not with the other, adding .05V may help.