Game freezes while mouse moving on dual monitors

[dananski]

So after many attempts to find out why games are so laggy for me and people playing with me, I think I've finally tracked it down.

If I have my secondary monitor enabled in the video settings, the entire game is frozen whenever the mouse is moved. The CPU goes up to 100% on core 0 and everything is frozen until I stop moving the mouse, then it carries on fine. When I disable the secondary monitor, everything seems to run smoothly.

I started noticing the problem myself around the time I applied the Windows 8.1 update, but I can't really be sure that's what did it. Has anyone else had this problem and/or know of a way to fix it? I really like this game in dual screen mode, but it kinda ruins the game if this happens.

My PC spec:
Intel i7-3770
AMD Radeon HD 5770
Samsung SSD 830 256GB
Windows 8.1
[Nothing else that could affect performance AFAIK.]

Things I've tried:
Lots of network stuff that was probably irrelevant now I've tested this offline.
Removed / disabled most software running in the background.
Turned off all monitors except the two I intend to use to play.
Turned down in game graphics settings a bit (I could try completely minimal, but it seems like there's something else going on here).
I have uninstalled my mouse software so that doesn't seem to be the problem.
Running the steam version - same problem.

On a side note, there was no indication as far as I could see that I was the one causing problems in multiplayer. If you're experiencing stutteryness in every game, but your ping seems fine, you might have this problem too.

[dananski]

OK, figured it out. AMD have a different driver for Windows 8.1 to the one for Windows 8.0 and it didn't get it automatically. Replaced the driver and all is good.