Ubuntu won't shutdown/restart

I've recently installed Ubuntu 11.04 onto a eMachine ER1402 Desktop.

I cannot get the system to properly shutdown or restart, whenever I select one of these the screen goes purple/grey-ish and just hangs. I'm quite new to using a linux os so not really sure how to start debugging this.

Just to note, the logout option works fine, Hibernate and suspend results in the system hanging.

I have tried using the terminal command sudo -h shutdown now, but it results in the same hanging behavour.

Thanks,

Chris.