Computer keeps stalling on boot and during few other tasks

[BlacqWolf]

I have just reinstalled a fresh copy of Ubuntu 11.04, and after I ran upgrade manager to obtain all the latest packages, my computer keeps stalling during boot and a few other tasks. During this - it does absolutely nothing - and for it to continue, I have to interact with it - press keys or touch the touchpad - and it'll work. Before the upgrade, it worked excellent. Now I have to press a bunch of random buttons and move the mouse in random directions for it to complete booting, shutdown and several other tasks while the machine is working (particularly tasks involving an optical disc - eg I have to keep doing this for the computer to run normally while burning a CD)

Any help would be greatly appreciated. Thanks