Laptop automatically reboots multiple times (Ubuntu 10.04)

[Jatin]

Hi

I just installed ubuntu 10.04 yesterday and everything was working fine. 
All hardwares recognised correctly and everything working fine. I later 
installed two apps namely k3b and VLC media player. I was watching a 
movie on my laptop using VLC reading from a DVD and my laptop rebooted 
automatically. This happened 5 times yesterday. Upon every re-start it 
was working fine for 15 mins then again it rebooted.

Can some one tell me what can the issue be ?

Also one more thing i noted is that my laptop was in a very hot state , 
could this have led to its reboot ?

Thanks
Jatin