system hangs on brand new build

Hey guys so im am having a whole bunch of system hangs on my new computer. it seems to be random because it happens even when i am only using firefox or some other low load program, it has also crashed when playing bioshock or crysis but it runs perfect on the settings for the entire time up untill it hangs (and yes it is hanging not crashing because i have to manually restart because it becomes unresponsive but i am not getting any error codes or reports because i dont get a full out crash) i have gotten 3 BSOD's since i have owned it but my big problem is the hangs cause they are much more frequent and annoying

i have run memtest86, i have the absolute newest drivers and have flashed my BIOS with the newest update and i have every update for vista that i can. PLEASE HELP ME. cause right now i am so frustrated with my Christmas present i am about to chunk it and build a new one.

I have thought it is maybe my GPU because it is pretty new (jsut released in Nov.) or maybe i dont have enough power in my supply but im not sure and i dont have a way to test either fo those things wihtout blowing alot of dough on a potential nonfix for the computer. I also think i may need to upgrade to the TF 560 AM2+ mobo cause my room mate has a newly built computer and he is using a similar (not the same but similar) setup and has no problems

My system is:
CPU: AMD Athlon 64 X2 4000+ 2.1 MHz Brisbane (AM2) (Stock cooling)
MOBO: Biostar TF520 AM2+
RAM: 2 GB G.Skill DDR2
GPU: ATI Radeon HD3850 256MB (OC'ed using Overdrive to 715 Core clock and 934 Mem)
PSU: Thermalke 430W PSU
Drive: Sony NEC DVD/DVDRW
OS: Vista Ultimate
Case: Coolermaster ATX

Set the memory voltage to 2.0-2.1v (PC6400) and adjust the memory timings to Mfg. specs in BIOS. Even if you have no errors running mememtest86, the fact your systenm crashes when running software in Windows strongly suggests memory is the cause of the crashes.