Used Ctrl-Alt-F6 in Linux, and can't get my screen back

Ctrl-Alt-F7 should work perhaps your X has crashed?

I just did what you did and F7 got it back for me, saying that before I remember X crashing and I had the same black screen

X is probably still running on F7, your display driver (or something else) is just misbehaving. You might be able to trick it into coming back on by going to F7 and blindly opening a terminal and playing with xset ($ xset dpms force on). Or you can ctrl-alt-backspace to kill X and GDM should restart it.

Try seeing if you can repeat the problem and then file a bug report (or let the lab admin know if it isn't your computer). It probably has something to do with your distro's kernel configuration/patching. I've had this happen before on Ubuntu but not any other distros (I've used many), which is why I am assuming it might be distro-specific issue. Probably the unintended consequences of some kernel patching.

I had the same issue. I tried with hitting ctl+ alt + F1 together. And it worked