Hi,
Put an XP (or whatever you use) disk in on start up,
and see if you can install your OS without formatting your disk.
If that fails, then the only way to backup your files before formatting is
to open it up, connect the harddrive to an other PC as a slave disk, and
backup your files from there.
This coupld be almost impossible with a laptop!

Last idea,get a USB or Firwire harddisk,
Install a hard disk onto that, and make it a Master,
then backup your files.
Use the CMOS menu.