My PC (XP) is stuck in a cycle of attempting to boot up. When I switch it on the screen gives me the choice of booting up in:

"safe mode
safe mode with networking
safe mode with command prompt
last known good configuration"

Whichever mode I choose the same thing happens the XP Logo briefly appears than an automatic chkdsk scan begins after this has completed a message says:

"config-list-failed"

"a problem has occured and Windows has been shutdown to protect your computer"

After this the screen gives me the choice of booting up in:
"safe mode
safe mode with networking
safe mode with command prompt
last known good configuration"


And so the cycle goes on

See if you can get into Safe Mode with Command Prompt, and follow the directions HERE to for a System Restore. If this doesn't work, you may have to boot to an XP install disc and perform a Repair reinstall.