On computer start up?

maybe the system crashed. then you will need to format your hard drive. Or you can try to log in to safe mode. When you turn it off and on and the computer is booting press F8 key for a few times until you get to menu on a black screen and it will show "safe mode" as one of the options, then you log in to windows. If that does not work, you will need your recovery CD put in and then restart the computer again and run the recovery program.