I had the same thing happen to me on my ASUS laptop and tried every method to counter it under the sun. The one that got the furthest was updating the kernel to 4.2.3, so if you want to give that a try then click here and follow the instructions.
Failing that, you can always fall back on SysRq, which is what I did. If you intend to use SysRq then really you should follow the REISUB steps, but really, if you need to do it often like I did, then all but B (or O in our case) don't really matter.
Hold down the
Shift keys and type in REISUO, making sure to wait about 5-10 seconds between each one and your computer will shut down.
R - Forces capturing of the keyboard
E - Terminates all processes
I - Kills all processes
S - Syncs all mounted drives
U - Remounts all drives in read-only mode
B - Reboots the system
O - Shuts down the system
It's because of the long wait needed between each entry that I cut down on the unnecessary ones; plus, most are only needed if you lose control over the system. So if you try to shut down manually and it freezes, as it is want to do, follow REISUO ... otherwise just use O.
(Remember that it won't happen right away, so don't keep pressing it to make it work faster; just be patient).
As an additional note: some computers may use different key combinations, such as
Prt Sc/SysRq. There are more details here on the Wikipedia page with alternate patterns you can try if the original doesn't work.
Hope this all helps.