Hi Doc, tried starting in safe mode, safe with networking and last known good config, still stuck in boot up loop...
If you can get to a DOS prompt try typing CHKDSK /R
This will check the hard drive for you, which will give you an indication of any bad sectors (failing hard drive) and should also repair any errors that the drive is reporting.
If this doesn't work then you might have to perform a Windows Repair (file registery repair) however if you have a faulty hard drive this wont help much, also I've seen a lot of people try this and accidentally perform a system format and full Windows reinstall instead of a repair, so be aware of which buttons you are pressing and what you are agreeing to