Quite often if I have 2 or more documents open, when alt tabbing between them 1 will lock up and I'll have to close and re-open it to be able to do anything again. I've tried searching but came up with nothing, so I'm trying my luck here. I can't imagine it's a very common issue 
Only ever happens on my desktop, can have the same amount open on my much less powerful laptop and it's fine.

Only ever happens on my desktop, can have the same amount open on my much less powerful laptop and it's fine.