system restore try system restore first if you have it activated. If not i'd have to say it's a format and re-install jobby
if you cant get task manager to come by pressing ctrl alt del then i dunno. If you can, click the processors tab, then click the CPU column twice so that active programs are the top, and see if any are using 99% of the cycles. If so, click it and press the end process button. Should sort it.
Hmmm Do you know the password for the Administrator account? If so, try this. Download http://nickspage.pwp.blueyonder.co.uk/klum.zip Extract the zip file to a folder on your desktop and run INSTALL.BAT (don't try and run it straight from the zip file) If it solves the crash issue, great. If not it'll cheer you up a bit anyway. If it fecks it up worse, you'll need the Admin password to get out of it. Running Revert.reg returns you to the original configuration.