Shutting a system down as you did, can cause problems, depending on how it effects the system.
Bassfisher refers to going back to a factory install, Which may be necessary, but there are some other things you could try first.
For instance, running chkdsk may repair corruption on your hard drive. Running it from safe mode is best.
If that does not help, try running a System File Checker, either from Safe Mode, or from offline. Use the command SFC /scannow, and the following link might help with the offline option.
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Let us know, and keep in mind, using the system restore might be an option.
Of course, a virus is always a consideration.