Wait until the utility analyses your Audio device for problems.
As far as I'm aware PT should work with W8.1, but there's always little things that get in the way. A conflict between the Windows Sound drivers and ASIO drivers This issue is confirmed. I'm looking at an RME FireFace 802 and have heard great things about RME drivers and support, but is Windows 8.1 the culprit here? I'd hate to spend so much (in excess of £1k) on an interface for it not to work with my system due to the operating system. They seem ridiculously expensive for what you get, and I would like something that would definitely have compatibility with EVERYTHING, not just "Pro Tools and maybe the rest". The fact that i've got it working with a Digidesign/Avid device, that also happens to be on the Avid approved interfaces list makes me wonder if I should buy Avid, but I'd really rather not. I'd also like to swap to USB as well, it's just easier and more reliable, plus the speed really isn't an issue nowadays. So, now i'm thinking I should upgrade my interface, preferably to something not Focusrite (unfortunately, because they've been good to me for the last few years). Could work as a temporary solution, but not long term. I've found an old Mbox 2 Mini around the house, downloaded the drivers, plugged it in and it works so far. Select the Input tab then delete any paths that are there, once all paths are deleted. Navigate to Protools, Setup menu and click I/O. Make sure you first select your Interface in Playback Engine. In the middle of sessions (between and in the middle of playback) I'll hear pops which mean the sample rate has changed - without me doing so! So then i'll get a message asking me to save, quit and relaunch, only upon relaunching it doesn't work. This procedure will set Pro Tools I/O to correspond with the Audio Device or Interface selected in Pro Tools Setup > Playback Engine at the time.
It's been getting progressively worse all week and today I just couldn't stand it.