My problem is that when i connect the 4-pin molex connector to the video card i get no video signal (black screen when computer is turned on). However, when i DON'T connect the molex connector everything seems to be ok. How can this be possible?
It was previously running on an Epox motherboard until i replaced it but the problem still remained. I also had a Chieftec 450W PSU but it started causing system instability (found memory errors with memtest86+) but switching the PSU made no difference either, The one i'm using now came actually with my computer case (dated way back). I have tried reseating the video card several times, also resetting CMOS and loading bios defaults. Nothing. I pretty much assume that it's some kind of an issue with the video card but can somebody explain how my system can work with the 4-pin molex connector disconnected from the PSU?
Just to make it clear, the molex you're using on the GPU is not a flat inline four pin molex, I believe it should be a 6 or 8 pin power connector. Also Restart it and go into the BIOS and make sure it's set to use the video card and not the on-board video first. Should be set to PCIe/VGA first, then the on-board AGP if no PCIe/AGP detected.
Power down the computer, plug in the video card power, unplug your video cable from the on-board video and plug it into the video card, start the computer making sure the BIOS is set to use the video card first and the on-board video second and hopefully that will solve your problem.