I just recently ran into a problem with my Sapphire R9 290 graphics cards. This is installed in a system and has been working well since November. Then a few days ago, I tried to turn it on and was only able to get through the first splash screen of the windows login process. So the BIOS showed up OK, then the small-blue window logo showed up and the white spinner below it, then the screen goes dark...and never comes back. My monitor didn't display any messages, but the LED light on it did start blinking - which indicates it has no video signal. This happened after the system had sat idle for a few weeks (I don't use it much, obviously). There's only one monitor involved here, and one video card.
After much going around and around with Windows stuff, I finally got something to work: I plugged my monitor into the HDMI output of the video card. Boom! Everything seems to be working fine. So my guess is that a high-resolution image is attempted to be output using the AMD driver (as opposed to some basic VGA signal/driver), the output stops working.
So why did the other output stop working? How can I switch it back on? I would rather use the DVI port that I had been using for 6 months - I don't have a spare cable or adapter. (I had one adapter, but I need that for another system that I do use frequently.)
Is there a default-port setting in the driver? I couldn't find anything like that. I believe that I tried the other DVI port and it also wasn't showing anything - I'll have to retest that.