Fedora random reboots and shutdowns!

[Nyan]

Hi all, I've installed fedora 11 (GNOME) on my laptop. It sometimes reboot itself. The screen goes black and reboots(sometimes just turn off!) Palimpsest Disk Utility reports HDD bad sector but when I run memtest, everything looks fine. Windows xp does not have this kind of problem before I use fedora. Please help me!!!

[Sagitter]

Note if you do particularly something when it happens. Also disconnect any external device and internet too.
Check if it still happens.

[Nyan]

I don't connect with any external device even mouse. only internet connection. Usually it happens when typing ?? Never happen when I'm not using it.

[Sagitter]

Try to change keyboard.