Windows 7: External Display Standby Problem [Freeze]

I have an ASUS F81SE laptop running Windows 7 x64 b.7127. This problem involves the connection of a BenQ T2200HD 22" LCD monitor (analog connection) and does not occur if the external monitor is disconnected.

Under power management settings, Windows 7 is set to turn off the monitor after 20 minutes and sleep after 30 minutes. After Windows 7 tells the monitor to sleep, the system is very slow to resume operation when a key is pressed or the mouse moved (the computer is NOT in sleep mode at this point, just the monitor). After 'waking up' **the cursor can move but everything else is frozen.** Sometimes the system will start functioning again after a few minutes, sometimes it won't and I have to force a hard reboot. Not good!

Windows is not reporting any device malfunctions in the error log, so I'm not sure what's going on. And it only occurs with the external monitor connected. Has anyone else experienced this problem?

Thanks so much,
G