Okee.. then
Connect a USB keyboard in there, or get into the machine using ssh.
Open a terminal, and run xev. It will show some stuff on screen (too much stuff, but don't worry). You will notice that it will show some more stuff if you move your mouse, as well.
Then, press the key combination you want to disable. The info in the screen will change, and you will have to look for the keycode value.
Run...
How To Fix Broadcom 4311 in Ubuntu 12.04/ 14.04
Written by Hakim
on January 19, 2015
Previously you check in terminal,
$ lspci | grep BCM
04:00.0 Network controller: Broadcom Corporation BCM4311 802.11b/g WLAN (rev 01)
If yes,continue to process this
1.Remove the BCM driver (standart SAT) in the kernel.
Go to terminal command:
$...