Crashes and cannot reinstall!!

I guess this is getting very complicated for me. I will explain from the beginning.

I have a laptop, Toshiba with windows vista as default windows. I recently upgraded it to windows 7 using an upgrade pack. I upgraded about 3 months ago. Everything was going fine till a few weeks ago, my laptop started restarting on its own. As soon as I used to start it, it used to get past the loading screen, and after a minute or so after I started using it, it used to restart. This used to happen a few times and then after a couple of restarts it used to work fine. I have posted before as well regarding the same issue and I was told to do a clean install.

Now this is what happened today: I put my windows 7 cd in started to do a clean install. I formatted both my partitions and while windows was getting installed my computer restarted again. I again went to set up and started reinstalling it. This happened a few times. To see if it some hardware issue I went to BIOS screen and left my computer on there for a few minutes. And it did not restart.

This time windows installation got completed. After it restarted itself (which it was supposed to), I got a error screen. (couldnt read the error screen as my laptop restarted again. Now this time it went to disk check, which I continued. Since then, for about 15 - 20 min most of the message was '' replacing orphaned files.....''. After that it said windows failed to restart. Now m running a windows memory diagnostic test.

Diagnostic test returned with the following reply:
File: \Windows\system32\config\system
Status: 0xc000000d
Info: Windows failed to load because the system registry file is missing, or corrupt.

It seems after a series of restarts windows 7 was finally reinstalled.... but I still have the same issue. My computer still restarts. Is there anyway I can revert it back to vista?