When you use an application in Windows like ntune to OC your card, that OC is ONLY APPLIED when you are in Windows.
Given that the 'missing operating system' error only occurs very early in the booting process, before Windows starts (obviously) there is no way that your card is being OC'd at the point you are getting this error.
I agree w/ people above saying that what must've happened is that when your system crashed, it corrupted some files needed for booting purposes. It's also possible to get this kind of error from a virus/trojan program that's messed with your boot files (like the bcd file in particular).
Anyways, go into your bios, and adjust the boot device order so that the CD/DVD drive is the first thing in the boot order.
Then put in the Windows disc, boot from it (it takes awhile), and choose to let Windows Setup repair your Windows installation.
Once it's done, you have to go back into your bios and set the Hard Drive to be the first device to boot from.
If this doesn't fix it ... I highly advise getting an adult who knows what they're doing with computers involved ... you going to need somebody physically there to help you Edited by brettjv - 2/22/11 at 5:50pm