I've had this system for a while now, probably nearing 2 years now, I have a GTX260 and I used to have a PSU of 650W Cooler Master, but got a new one couple of days ago of 600W (Also cooler master). My PC won't boot if I connect the GPU to the 6pin power connectors, if I remove it, or disconnect the 6pins my PC boots no problem. (Except no monitor signal if GPU isn't connected, which is logical). I'm not sure why this is happening now however, i've had the system with the 650W for almost 2 years, but one morning it just wouldn't boot, I replaced the PSU with the 600W one and still won't work, any ideas? Help would very much be appreciated!
Btw Zombiemodd's problem was unsolved, but best suggestion was upgrading his PSU (he had 500W shitty one), but mine's good quality and above what is required for the GTX260...
More about :faulty pci 6pin power problem zombiemodd psu
If it won't work with two different PSUs that indicates that there is probably something wrong with the video card. Either that, or you have really bad luck with power supplies. If you have another video card lying around, try that one and see if it will let your machine boot while connected. Otherwise, you may want to get a power supply tester or a multimeter and make sure that the both of them are actually delivering 12V on the +12V rail.