You can use the System Recovery software that you made when the computer was new. Also, depending on the age of the computer, you can use HP Recovery Manager. In either case, you would choose the option not to save your files.
For future reference, when requesting help you should always include the make/model (i.e. p6-xxxx) of the computer and/or monitor. This information is necessary for us to review the specifications of them.
Please click the Thumbs up + button if I have helped you and click Accept as Solution if your problem is solved.
I am not an HP Employee!! Intelligence is God given. Wisdom is the sum of our mistakes!!