[Staffslug] Ubuntu 9.10 just switches off!

I dual boot Ubuntu 9.10 and Windows 7 on my Toshiba L40 Satellite laptop with T2330 Dual core 1.6 GHz processor and 2GB RAM. While booted into Ubuntu, it will suddenly go "click"! and immediately switch off. It even did this once at the end of the install! Needless to say it doesn't happen in Windows 7. Anyone had any experience of this or know how to fix it?