I didn't install 10.9.3 (I'm at 10.9.2). I went ahead and told it to install 10.9.4 in the update. I clicked on the restart now button. It exited the AppStore thing and sat there and did NOTHING. I tried it again. NOTHING. I manually told the computer to just plain restart from the Apple icon. NOTHING. It just sits there like I never told it to do anything at all. I see no activity what-so-ever in the Activity Manager to think that it's updating in the background or doing a darn thing. I'm afraid to force the computer down under these circumstances. What is going on here? I've never seen it behave like this in any upgrade since I got a Mac. Panic before/after an update, yes. Do NOTHING? No.