PSU/GPU upgrade gone awry

So I've been carefully planning the upgrading of my media center HTPC into a reasonably nice gaming PC. It's a Dell XPS 8500 with i7, 16GB RAM, all the fixins. Today I finally pulled the trigger and installed a EVGA GTX670 along with a Corsair TX650M psu. I chose those after lots of online research including confirming that others had installed those into the same model computer. It was a tight fit but I got it all in there and it wouldn't turn on. After some troubleshooting I realized I didn't have the 4-pin CPU power cable hooked up right, and after changing that it booted up and worked fine. I downloaded the nvidia driver updates, watched a video, then had to go put the kid down for the night. I came back a few hours later and it was off and wouldn't turn on. I turned the power supply switch on and off, and since then it'll turn on but only to run all fans at full speed-- no video output, no boot into windows or bios, just the fans at full strength.

I'm new to the PC world and have only a basic knowledge of what I'm doing so I'm not sure I can fix it myself, but does that sound like anything recognizable? Did I fry my CPU or do I just have something hooked up wrong? Thanks for any help.