Does your Windows computer shut off when you turn it on? If you have tried pressing the F8 key and tried all safe mode options, as well as the system restore feature, and nothing helped, there are other trouble shooting options.
I assume you have tried "Last known configuration" when hitting the F8 key. Also, when selecting any of the safe mode options does the computer boot into safe mode successfully or does the computer power itself off again? If the computer boots successfully into safe mode with networking I reccomend running some virus and malware scans.
If you have the Windows Vista installation media ie. DVD or restore cd that came with your computer, you can do a repair installation. You can follow the tutorial for that.
If you don't have a recovery CD or Vista DVD you can download a windows vista recovery disk via the following link.
The file is an iso file so you will have to burn the iso file onto a CD and make it bootable. There is a tutorial on how to do this if you don't know how.
These solutions would also work with other versions of Microsoft windows, for example XP and Windows 7.