I have three screens connected to a Radeon 6850 card. Two are connected via DVI and the third is plugged into the DisplayPort using an active DisplayPort to DVI adapter. The adapter has a USB cable that plugs into the motherboard to give it power.
Strangely, all three displays work perfectly fine if I don't plug the USB power cable into anything. Why is this, and will it stop working if I stress the graphics?
Also, for some reason if I do plug the USB power cable in, the DisplayPort screen dies whenever I plug my external HDD in. I thought this was power issue - but without the DisplayPort power plugged in everything (including the HDD) works fine.