how can i reboot a laptop without a disk?

I don';t hinik that you mean "reboot" because "booting" (From the technical term: "bootstrap loader".) happens every time you switch the PC on.

If you mean you want to reload the Operating System (Windows? You don't say.), some models of PC have a recovery partition on the hard disk but others require a "Recovery Disk". It depends on the model of the PC and you don't say what you have.

BTW its LAPTOP.

T
January 2011