Help: I can't open Quickbooks at all...

I hope someone can help me with this problem. I have a VPN set up between 2 users with 2 QB Pro 2005 licenses. When the "power" user or administrator login was done from one user, the other user could not even open the program at all the next day. It just freezes with no error msgs. ALL programs were removed and re-installed on the computer in question to NO AVAIL. Please, I've searched all over to find help on this and the QB Help Desk are no help, and then want $250! Can anyone tell me what's wrong here???