google : If you did not make the "recovery disks", and your system has a dedicated recovery partition (most new HP's have), you might want to try pressing F11 or F1 depending on your system, during boot (post) [a message on the botton part of the screen just when you press the ON button appears telling the user which key should be pressed in order to lauch recovery. Please check - it's usually DEL or one of the F keys.] . Then, system will boot from the recovery partition, and you will be able to restore factory settings. Additionally, if you can boot on Windows (original installation), go to HP Recovery Manager and select "Andvanced Settings">"Recover your computer to it's factory conditions"

keď budeme vedieť model, nájdeme k nemu manuál a v manuáli bude konkrétny postup.