I did an auto install of R5E50 on a Dell Dimension 8200 with a P4 1.8, 128 mb ram, pvr-150 and a geforce 2 mx400. It works at first but every time I stop watching tv and go to the menu when I try to go back to tv it says it can't connect to the backend. I have to manually start it by typing "mythbackend" into a terminal. I am a complete noob when it comes to Linux so if you need more info please tell me how to get it.

It's a known problem, see TJC's upgrade notes.
If you have a keyboard, press Alt+3, count to 15, and then the backend should restart.