Will it boot in safe mode?
Do you have a recovery disk?
What is your operating system ?
If you turn on the computer and repeatedly press the F11 key, about once every second, your Recovery Manager should open.
Under I need help immediately, click System Recovery.
When System Recovery prompts you to back up your files, select a backup option.
If you have already backed up personal files or you do not want to back up personal files, select Recover without backing up your files, and then click Next. Continue to the next step.