Ihave a problem to install kaspersky antivirus So I want to reboot my computer.

I assume by reboot, you mean to restore. In order to restore, or re-install Windows, you need the disc or a recovery partition. If you have a recovery partition, when you start your computer up and during POST (the black and white screen with text), you should see something like, "Press F12 to enter Recovery Mode". Do so and follow the steps. But this usually only applies to manufactured computers like HPs.