scanning my laptop  

Hello emine08,
There is probably a bad cluster in your hdd. Run a defragmenter or open a dos console window and type :

chkdsk /r

Wait and reboot after the process is finished.

If it starts again during a scan, download a Linux LiveCD with an antivirus. You can search the net for Hacao Linux 2009 CE : it is a free English/Vietnamese Linux especially made for laptops and it comes with XF-Prot (a free Linux version of the commercial F-Prot) installed. Burn a CD with the ISO image, run it and scan your hdd with XF-Prot under Linux.
I hope this helps you.

I think with some laptop it happens, it happened with my laptop at the very beginning, Whenever I would start scanning it would complete it and then restart the laptop itself,then I had it given to my friend to check it out, he did something maybe the settings problem and now its good, I think if you do not know something about it so better ask someone to check it out.