ok I have no idea what to do heres the problem.

My parents have a Mac Mini and they asked me if they could fix the problem they were having. When you start it up it boots to the login screen and as soon as you login into any account the monitor display input not supported how can I fix this without going into the system preferences? I tried changing the resolution on the monitor but that didn't work either, and they cant find the Tiger disc am I screwed?

thanks in advance for the support.

Looks like the resolution somehow get messed up. Try and connect another monitor to it and set the resolution that fits for the monitor theyre using.