Hi,
I'm not sure from your message whether its ok now or not? After you reformatted, I mean...
If its not, then you have a few options.
The first thing to try is to boot to "last known good" configuration. This will overcome any registry ordriver problems that are causing your system to fail. At least ones that crept in since your last successful boot.
Secondly can use an emergency repair disk to correct the problem. But if you haven't made one of those and kept it up to date then...
Thirdly you can boot with the original CD and choose the repair option off that to fix any problems. This resets many of the registry settings, though and you will likely lose some of your installed programs.
Fourthly, you can install again over the top of the old installation.
And finally, you can rebuild from scratch.
Hope this helps,
Cheers,
Tim.