I recently installed Ubuntu 10.04 on my MacBook. I have it running smoothly on here, but when I used the same disk to install Ubuntu on a friend's Dell Laptop it isn't working correctly.

After the installation process finished, he logged in and everything ran just fine. However when he shut the computer down and later turned it back on, he can't log on. He's using the same login information as before but he keeps getting an authorization failure. I've had him try using his short username and the full name but neither will work.

Is this a hardware problem because of his computer or did something go wrong with the installation?