Well, your question sucks because you don't mention if one of the keys works, and one of them doesnt. The reason I say this is because based on the code you posted, you're checking
twice. If that's really what your code is doing, you'll never know when
Furthermore, if you press the one of the windows keys, doesn't Windows display the start menu? How can you possibly think using a key combination that involves the windows key is a good idea?
If you insist on pursuing this, look at WPF
CommandParameter="You pressed 'F5'"/>