Computer help forum: Switching between laptop display and external monitor

Apology in advance for this LONG post, but I am not the most technically savvy person, so I'm explaining the long way.

I am running a Dell Latitude notebook and a Gateway tower (both on Windows XP Professional) off a ConnectPro Master-IT USB KVM switch, so they share my Samsung SyncMaster 150MP monitor and Microsoft wireless keyboard/mouse. Normally I run the laptop with the lid closed, only active display being the Samsung.

I sometimes need to disconnect the Dell to use it in other rooms, and therein lies my problem. The Display Properties tab shows two monitors: #1 being my Samsung and #2 being the Dell's display. I tried adjusting the Display Settings to make #2 the Primary display (thinking I would just switch it back, if needed, when I reconnected the Dell to the KVM), but when I do this, I lose the Samsung AND the Dell displays, whether I hit APPLY or OKAY. I end up having to shut the laptop off via power button since I cannot even navigate to the Start > Shutdown buttons. I power it down, disconnect the KVM cables and restart it, and I get my startup and log-in screen. Five seconds after I log in and get my Windows desktop, the screen goes black (indicating to me that the Dell's BIOS recognizes the Dell display as Primary but once Windows takes over, it applies a different setting).

Of course, once I reconnect the KVM cables (no need to restart), the Dell's desktop pops right up on the Samsung (along with any menus generated by my random frustrated keystrokes on the Dell's keyboard). When I re-open Display properties, they've been reset back to the Samsung as the Primary monitor (WTF??).

I KNOW there is a way for this to work, because I did it yesterday - carried the laptop upsatirs and worked with no snags for 4 hours (racking my brain to figure out what I did differently). But the Dell went into standby/sleep mode for several hours (I closed the program I was in, but didn't shut down before leaving the house). Came back to a sleeping Dell. After a few failed attempts to get it to wake up (not realizing that it WAS awake and responding to my keystrokes even though I couldn't see it), I shut it down and restarted, and thus began the cycle of Turn On - Log In - Windows Desktop Appears - Screen Goes Black.

Isn't there a way to set it so that the Dell automatically reverts to its own display when not connected to the switch, and failing that, how do I manually switch back and forth between them in a way that ''sticks?'' I'm pretty sure I've inadvertently triggered this via Display Settings, but I cannot figure out HOW, or how to undo it. Thank you in advance for ANY help.