What OS (Operating system) are you running?
If its windows vista its a common problem...If its XP it does happen time to time, Skua is correct, Your OS has gone corrupt (Either a file missing or a virus has deleted a system file)
The only way to fix this is insert the OS disk and reinstall the OS (Most likly you will lose everything on the computer) but sometimes there is a repair option which keeps ur files....Just fix's the OS,
Another option is to take it to a computer shop and get them to back up the HDD then get them to reinstall the OS (Will cost you roughly around $150)
If you have any questions please ask
21/08/2007
www.camlew.com | Melbourne, Victoria