Worst cases - 1) CD Drive dying, 2) Hard drive dying, 3) laptop fried
try the first 2 before anything else, to check the CD, burn a bootable CD with something like spinrite or a live linux distro on it, boot from it and see if it reads without errors.
If it works, try the HD, spinrite will do that
GRC's Website
If it's the CD Drive, they are under £100, if it's the HD, spoton have them for around £45, both are cheaper than a new system.