Help would be greatly appreciated

[donchef]

I had windows 98. i purchased a broadband modem which I was attempting to install. However I found that I had misplaced my Certificate of authenticy. I decided to upgrade to windows XP. On installing this it detected a problem. "It says to check for virus on computer, remove any newly installed hard drive or hard drive controllers. Check your hard drive to make sure that it is properly configured and terminated" I cannot start windows and get a blue screen with this message each time. The last known configuration does not work and places me back in the same circumstances. I believe that it may be due to attempted installing of modem? How can i fix this as i cannot seem to be able to get anything but this blue screen.
Kind regards
Donagh
Ps Im afraid that i dont have a great degree of knowledge so basic instructions if possible. Thanks