I've configured my laptop to be "dual-head", that is, I have attached an external monitor, and display information both on my laptop's screen, and the external monitor.

Whenever I close the screen, the laptop switches to displaying my desktop onto the external monitor. That's all well and good.

The problem comes when I reopen the lid. The primary monitor reverts to the laptop screen, but the external monitor is not re-enabled. To re-enable the monitor I have to muck around via Start / Settings / Control Panel / Display / Settings.

To eliminate this problem, I installed res_set in C:\WINDOWS, and created the following batch file:

res_set -m 0 --max
res_set -m 1 --min
res_set -m 1 -x 352 -y -1024 --max

I named this file C:\WINDOWS\fix_res.cmd. I then created a shortcut to this file, and installed it in my QuickLaunch bar, in my taskbar.

The first line resets monitor 0 (my laptop's screen) to the maximum resolution and bit depth.
The second line resets monitor 1 (the external monitor) to the mininum resolution and bit depth. It could be any setting other than the setting I am next going to set it to. It just needs to be different.
The third line sets monitor 1 to the maximum resolution and bit depth, and positions it at X-position 352 and Y-position of -1024 relative to monitor 0. You can see these numbers by positioning the 2nd monitor as you like and then execute the command:

res_set -m 1 -q