Since no one replied, I assume no one has suggestion. And after 5 hours, I found a solution.
I restored an older Maya profile I saved a long time agog back to C:\Document and Settings, assume something in my user configure file is messing with something...and then Fcheck works!
I have no clue what caused Fcheck to not pop up, I never messed with its setting at all until yesterday. So I couldn't have changed a Maya settings that caused Fcheck not pop up.
Edit: After 3 more hours, I replaced each file in pref one by one, and tracked down the file that cause my Fcheck not popup. It is userHotkeys!! Why would userHotkeys file caused Fcheck not to popup after PlayBlast? God knows, maybe Maya programmers can tell me. It's very frustrating that something so unrelated can cause another part of Maya to not work....
When I searched other posts for how other users solve this problem, it seems there are a few others experienced this problem in the past but can't solve it either. So I suggest you try my method if you run into this.
I guess it's good habit to keep your old profiles around, you never know what whacky things Maya can do.