thunderbolt display goes black, forcing manual restart
I have a 27" TB display with AMD FirePro D500 3072 MB Graphics connected to my MacPro (2013) on El Capitan (v. 10.11.3). The TB Firmware is up to date.
Occasionally, while in Safari, the TB display will unexpectedly go black and stay there. I have to power down the MP manually and then reboot. I used to think this was a Parallels problem (where I was running a virtual Windows 10 machine), so I have shut down Parallels unless I specifically have to use Windows. Today, with Parallels shut down, while logging into a website (msevensoftware.com), the TB display went black. Again I had to manually shut down the MP, then restart to clear.
Thunderbolt Display (27-inch), OS X Mavericks (10.9.2)