I setup an Ubuntu box in my company's breakroom for internet browsing. It's running 8.04 and auto logs into an account with limited access.

Here's my problem. Whenever I try to logoff, reboot, change users, or shutdown, I just get a black screen. I've googled and other people seem to have the same issue, but they all seem to be using ATI cards and I'm just using onboard video.

The black screens don't bother me that much, but I would like to be able to login to the admin account to update the system and install new packages. I don't know that much about Linux, so any help would be appreciated. Is there a certain key combination I can hold on startup to avoid the auto login?