AMD Radeon x1950 Pro stopped working

Hi, i have a Dimension e521 desktop, and tried to run a Nvidia 9800GT on it. Unfortunately, the computer did not detect the 9800GT so i traded with a friend for his radeonx1950 pro. As soon as i plugged it in, the computer detected it, i installed drivers, etc etc (and i was freaking happy). However, 2 weeks later, upon turning on the computer, i got a blank screen. The graphics card fan was still spinning, but i could only get a signal by plugging into the onboard graphics card with no drivers (very ugly resolution). In device manager, the computer does no detect the radeon, and yes the bios is turned to auto, and the onboard 6150LE is disabled still. After much research, i tried replacing my 300watt PSU to a 500watt. But, still no response  . It seems like amd and nvidia cards hate me, any ideas guys? and if it is a MB problem, how can i test it to be sure? maybe somewhere along the way i messed up my drivers?