Reboot looping after driver fix

After reinstalling the bios and network drivers to get my system back on the net after a hard drive replacement and windows 7 reinstall,  

http://en.community.dell.com/support-forums/desktop/f/3514/p/19654017/20825923#20825923

my system has a new problem :

It is rebooting over and over, lIke it is in a loop.

It reboots, then does it again before windows finishes starting.

Then it shuts down.

When I restart,  it goes into repair mode. I have to wait until it stops, then it starts windows properly, but says the computer recovered from a serious error.

What has happened,  and how do I fix this?

Thanks.