boot up and go to bios configuration first
- set the system clock to some time in the past (but not a day BEFORE the last day you used it)
Reboot and allow to come up (but dont have it connected to the internet)
copy off or transfer the files you need
reboot from a reinstall cd of something current..
reformat the pc.
sorted!
-- Or you can download and burn: Puppy Linux, and boot from that. Within a minute, you can be browsing the web, internet...the works from the pc