Try to System Restore to a date/time prior to when the problem began. Start > Programs > Accessories > System tools > click on System Restore > follow the prompts.

A non-destructive System Recovery. Go to Start > Programs > System recovery > Click on System recovery > follow the prompts. This may require re-downloading/installing MS Updates.

Another option may be sfc /scannow. Go to Start > Programs > Accessories > Command Prompt. Type "sfc /scannow" w/o the quotes and press Enter. Note that there is a space between "sfc" and "/scannow". This can take a half hour or longer, so be patient.

Hope this is helpful.