Screen freeze after waking up

view full story

http://askubuntu.com – Ubuntu 11.10 64 bit on Dell Optiplex. I'm using Synergy but I'm not sure the problem is related to it. The screen freezes after coming back from screen saver. (It's not suspend because my Power setting is Don't suspend.) The blank screen turned back to the last screen I used but no response. Mouse is still moving. Keyboard works as I can drop down to terminal using ctrl-alt-f1. Other services seems to be working by remotely logging in. I found a temporary solution from web. Turn to the terminal using Ctrl-alt-F1. After log in, type unity --replace & Back to x windows by ctrl-alt (HowTos)