You should really check your power manager settings to make sure you are actually giving the laptop a break. A lot of the defaults are set for desktops really. It is why I was calling for a laptop distro for lubuntu... alas I got tumbleweed.
If that doesn't work try this: **Correction: sorry I had not picked up your graphic card was not a nvidia card. Please follow the instruction in the linked reference for information on how to install for radian. Unfortunately, it is a bit more long winded. Make sure you download for 64bit if that is what your distro is (and vice versa)
EDIT: After re-reading your post I am quite sure that it is more likely to be your power manager settings causing the issue. Either way install the latest driver though, but check your power first so you know for future reference.
EDIT: Go to start>applications>power manager
If you cannot find it yours will be either
Is my guess, but if you can't find it, go into synaptic and search power and tell me which ones are ticked.
power manager basically allows you to configure the default settings for your battery. I have mine on suspend when the lid is closed or when I am not using it. I am using the xfe one. Let me know how that goes.
Link to my blog page with screen shots
Be careful when installing packages too. Always check they are right for your version. Ubuntu sort of dump them all in once place and leave it to us to check.