Think your best bet here is the system file checker first.
Start / Run / type in the run box sfc /scannow (note the space) this may take a while.
If still no joy,i would suggest if possible a restore or recovery from the partition if it is availble.
F11 on startup may give you the partition and 3 options...think i would go for the restore to factory settings and start from scratch,this assuming it has the restore function on the partition.
Obviously if you can,back up what is needed first.
Hope this helps.