You can do a nondestructive system rebuild instead.( worth a try)
Basically you boot from the DVD/CD and do everything like you were going to do a new install. You have to ignore the first repair window and wait in till you choose the partition to install to. Then the installer will find the old system already installed there and give you the option to reformat(DON'T) or repair the existing system. Choosing this repair option will reinstall only system drivers etc. needed to boot leaving all your documents, app and settings untouched.
You will need to reenter your S# at the end of the rebuild just like you would a reinstall.
This is much faster than doing a clean install and you don't have to reinstall all your apps.
XP and Vista can do this. Very handy when a virus rapes you system and you can't boot anymore. Most people get led astray by the first repair window that is for users that have a backup system in place and/or can edit the system files themselves. Most don't/can't.
Note you will have to use system update to get current again unless you had the foresight to create a 'slipstream' boot disk. Slipstream disks have all the service packs and updates incorporated into a windows system installer disk so you only need the updates that came out since you made the disk.