Computer crashing every hour or two, internet issues, maybe related.

Hi. I'm having some problems with my computer. They may or may not be related. About 2 days ago, my computer started crashing about once every 1-2 hrs. Something starts spinning up inside, then 2 or 3 seconds later it shuts off. Black screen, sometimes it reboots, sometimes just powers down. Does it even when I'm afk with nothing running, no load. In addition, a little while after this started happening, I started losing internet connectivity on some of my programs. Games work, ventrilo, etc, but my internet browsers and autoupdaters don't. I've tried running all the antivirus and registry programs I can find, but nothing's worked so far. It seems like the kind of thing a virus would do.
I'm running Windows 7.

Dell Dimension 9100
Pentium D 840 2.8ghz
Nvidia 9800 GTX
3gb ram

Any help you can give would be appreciated. Thanks!

Honestly it doesn't really sound like a virus. If indeed you are running the Windows 7 beta, and not the Release Candidate (get it here if you are: http://tinyurl.com/832nco ), then Bullheaded's statement holds true. Other than that, it sounds like possibly you have a failing component or your system is overheating. Also, have you installed any new programs recently. Rather than a virus, it may be caused by some malfunctioning software blue-screening your system. There are dozens of possible reasons. If you gather up more information (check your event logs, look for crash dumps, etc) and you post it up over at the official Windows 7 RC Support Forum located here http://tinyurl.com/9fhdl5