Issue with new build - Continuous reboot

I'm not sure if this belongs here or in the software section, but I thought I would throw it out there.

I just built my new PC and have done:
1) Installed Vista and all hardware drivers (got the latest version from the web)
2) Ran memtest on Memory (all good)
3) Ran Prime CPU stress test (through vista)
4) Installed dual boot Windows 7 beta

The issue for me comes in on the Windows7 beta. The system seems to be stable on Vista, but when I boot Windows7 some funny things start happening and I'm not sure if it's something wrong with my build, or with the OS (it is a beta, so I'm not expecting perfection). Here's what happens:
- The machine seems to run Windows7 well while you are interacting with it, however when you leave it alone and it goes into sleep or hibernate (not sure which) the system completely crashes and tries to reboot itself continuously. It never makes it to the POST. The fans will turn off for a few seconds and then back off. There is no activity on screen so I'm not even sure what it's doing. If I do a hard re-boot then it boots back up normally and asks which OS I want to load. This never happens with Vista, but I can't imagine why it would happen with 7beta.

I'm fine running Vista for now if it truly is a software/OS issue, but I want to make sure there's nothing wrong with my set-up before I write off the 7 beta. If I can get the 7beta stable I'd prefer to use that, since it works better with my QAM cable tuners.

Any thoughts?