I brought my Mac Pro home from the office tonight for the weekend-- something I have done several times before, keeping it in a padded camera bag that fits it snugly. No drops, no bumps, even took a car home instead of the subway. Now that I've plugged it in and connected it to my Thunderbolt display, it won't show anything on the screen. It's not a blank screen or anything-- it's just as if the monitor weren't connected. However, all the peripherals plugged into the display lit up when I connected it (my wacom tablet and a hard drive). The display just stays off. More worrying is that the fan is blowing at full force as if it's rendering something huge. I got the startup chime and the power lights around all the ports, but like I said, there's no picture to see. I did recently have the graphics card upgraded (swapped from a different machine at work) but that was several days ago and I have been using it with no problems since then. I've also plugged in my laptop to the display, and it works (that's how I'm viewing MR currently). I'm terrified. This beast was like $10k and it took me forever to convince the accounting team to buy it. Any ideas? One time I couldn't get my MacBook to work with the monitor and it was because a driver was out of date. Doesn't explain why the fan hasn't stopped blowing for the last 5-10 minutes. Edit: I'm running Yosemite, but since I can't get the display to connect I can't tell you what version. It's a 2.7GHz 12-core with 64GB of RAM (2x32GB OWC) and the dual 6GB video cards.