A lot of those components will generate a lot of heat, and if you don't have adequate ventilation on your system, could cause problems much like you're having.
Try running the system with the case off to see if the increased air flow does anything to help.
I am currently running Windows XP x64 with an AMD x2 3800, Seagate HD, Lite-On Media Drive, 1.5G RAM, 7600GS GPU, and BFG 650 PSU.
For about 2 months now I have been having difficulty with my computer. I was dual-booting XP Pro x86, and Vista x64, but both had a tendency to hang while on the Splash Screen (XP more than Vista), and would turn off in the middle of projects and games, so I replaced my 400w PSU with my current 650w. Fixed the shutting down, but the computer would still stall on startup. I flashed the BIOS, but still the same problem. I decided to scratch my HD and start over, and this time tried XP x64... same problem on splash screen, but now it will hang in the middle of games, and sometimes even internet browsing. I thought the problem might be with my GPU, but I replaced the 6600 I had, with a 7600GS... once again, same problem. The symptoms seem to match those of a PC that's been overclocked beyond it's means, but right now I have everything running at Factory Settings and it still hangs. I know it seems like a rather trivial, but I have exahusted all my resources and still no good. Any One have any other ideas?
PS: Does Nvidia nTune usually work well with x64, because I had that installed for a breif day or two.