There's a few things you can try to fix this problem.
1. As soon as you turn on your computer hold F8 if it's a Dell or possibly F12, F2, or ESC. Before the Vista loading screen appears you will come to a screen asking what mode you want to boot into. Pick Safe Mode with Networking. If you can get in, run the free version of the program Malwarebytes which can be found here
as it may be a virus that is causing the OS malfunction.
2. If Malwarebytes does not fix the problem, when you are asked to do a system restore, pick a restore point further back than the one you keep picking. It may be that the cause of the problem happened before the system restore point you're picking and picking an older one may fix it.
3. If all else fails try to get into your computer using Safe Mode with Networking again. Then use an external hard drive or something to back up all of your data that you need. Then insert the Vista setup CD and boot from CD which can be done by holding down F12 if a Dell or F2, ESC, or F8 when booting. Try running the setup utility on the CD and if that does not fix the problem delete your partition on your hard drive and reinstall the OS. Then use your backup to get all your files back.
Good luck and thanks for using Fix Ya.