If you have a windows installation disk that came with your computer. You can boot from that disk and try to do repairs.
To boot from the disk you press a button (e.g. F12 or F8) when you first start the computer with the disk in. It will say what button to press on the upper right hand side. You will have only a couple of seconds to press it.
Once you do, you can then choose CD/DVD Rom of something like that from the list using the up and down arrow keys and the enter key.
It will then start as though its installing windows 7. Then at a certain point after following some of the instructions you should see a small clickable for “Repair windows”. This should help you scan your system and fix any problems related to the Operating System.
If you do not have the windows 7 installation disk, you can download the image for it from many places and burn it onto a disk.