TF2 Crashes in Windows 8.1

I just upgraded to Windows 8.1 and now TF2 doesn't work. I load it and then after about 10 seconds it crashes to desktop with no error message and without freezing. It just closes. 

My graphics driver is up to date. Any ideas on how to fix? Apparently some people were saying it was down to a 3rd party anti-virus but I have had the anti-virus on my computer since the beginning (Symantec EndPoint Protection) and TF2 has always worked. 

Help is greatly appreciated!

System: Asus Q550LF, i7-4500U, 8GB RAM, nVidia 745M, WIndows 8.1

Try to run it in compatibility mode with windows 8 and defragment the game cache.

Verify integrity of game cache. TF2 is a buggy game..it doesn't run well in windows 8 for me, same story with windows 7 before that

Tried almost everything including all of that. Got it to finally work. I had to uninstall and reinstall Steam.