how to awake second display after sleep?

We have win 7x64 ultimate systems all with dual monitors in several floors in this building.
We often turn the system to sleep when we go to meetings. When we return, we awake the system, but only the dispaly #1 will be active, and #2 display will be black. We can only get display #2 to be active, after we shut down the system and boot the system on again.
These systems were running Vista before, and dual displays awake active after sleep.
What can we do to make display #2 active?

Right click. Go to screen resolution. Click detect. Done.

we have tried multiple time and failed on every systems upgraded from Vista to Win 7x64 ultimate.

yes, awake from sleep, we right click, screen resolution, click detect. right side screen #1 active, screen #2 still black. Only way to make screen #2 active is to shut down system, and reboot again.

What GPU is the system running?

many different systems, Dell, HP, Acers, Gateway,...etc.
starting to upgrade from Vista to Win 7 X 64 ultimate.

The one I am testing is Intel Celeron Duo CUP 3.06GHz, 4GB,
Display adapter is NVIDA GeForce 6200 LE, Microsoft WDDM driver.

For this test system, it uses NVIDIA - 257.21 desktop win7-winvista-64bit-English-whql.exe driver - downloaded recently at Nvidia web site for the Nvidia Geforce 6200 LE display adapter.

We found this Nvidia GeForce 6200 LE display adapter's two output sockets (EGA + DVI) behave differently after awaken from sleep.

1. EGA to display #1, DVI to display #2.
after awake from sleep, display #1 works, #2 will be black. In "Control Panel" display, still sense and detect two monitors. As soon as we unplug display #2 (even it is black), control panel will show only one main display available.

2. EGA to display #2, DVI to display #1. Win 7 will automatically select display #1 as main display.
after awake from sleep, display #1 & #2 both are black. After we unplug display #1 from DVI socket, monitor #2 will turn back on showing system of one one main display available.

We do not have this problem with XP and Vista, we only have this problem with Win 7x64.

We ran Trend Micro HijackThis v2.04, scan log shows:
023-Service: NVIDIA Display Driver Service (nvsvc) - unknown owner - C:\Windows\system32\nvvsvc.exe (file missing)
is this because this is Win7-x64 system and NVIDIA driver is getting confused?

Also, if the monitors are turned off because of power Option setting, both display will awaken without any problem.
Also, if we turn the monitor power off, it will continue working when power turn back on.