Registry/Configuration error, Windows won't boot

My Dimension XPS 450 Windows 98 has a problem! (PII 450, 128mb RAM)

Windows does not boot up to start with, so i cannot do anything via Windows. I am left with the Start Up mode selction screen - Normal, Logged, Safe Mode, Step-By-Step Confirmation, Command Prompt Only, Safe Mode Command Prompt Only. When selecting safe mode or normal, the computer hangs whilst windows is loading.

As the message "Windows has detected a registry/configuration error. Choose, Command prompt only, and run Scanreg" appears on screen with the startup menu, I presume there is a problem with the registry. Running Scanreg does not work, as it hangs right at the beginning whilst it is checking system files.

Looking at responses to other people who have had this problem on the Dell Community Forum, it appears one solution is to restore a working registry from a few days back. Can you please advise me if this is the correct way to proceed.

Having emailed Dell themselves I have been told to clear out the Startup environment via WIndows - but windows wont boot! also suggested was to reinstall Windows and delete the hard drive partitions, but I am reluctant to do that as I haven't had a chance to back up my hard disk.

Also, does this problem have anything to do with the fact that whilst running the Dell Diagnostocs disk to try to correct the problem I was told that the computer had failed the "USB register Test - USB1" and "Register #0 read/write failed Found :0x006c Expected :0x0000" On a second run it said it found "0x0542"? I had assumed that the USB drives where not anything to do with the registry.

Thanks