Operating system not found

Here is a link to your problem, its kind of high tech stuff, http://support.microsoft.com/kb/321626

You might want to try putting your windows cd in the drive and restart you computer, hopefully it should boot up off the disk, than you can click 'Fix errors' or something like that. You could also reinstall windows, but you well loose all your data. Good luck and me know how you made out. And please rate mty answer.

Perhaps your hard disk is not the first device. Maybe there is no need to reinstall Windows and definitely to lose data.

Can you open BIOS settings and check if hard disk is the first boot device?