RR?

I am having a problem with my dual monitor setup.

OK. Dual monitors. You don't have a "further" monitor and external monitor? Just 2 monitors? Yes? You haven't a 3rd screen that you may use for colour correction? Something like an old TV or pro high-res monitor?

I can get my computer monitor and an external monitor working, but they both show the same thing.

Eh? DUAL and EXTERNAL is not the same. An external monitor is one that is fed via a DV>AV converter.

In the past I have been able slide my Preview window off onto the external monitor, but this is not working now.

I can't! I can't slide my Windows onto my external analogue Monitor? However, I CAN use my 2nd Monitor as a PREVIEW monitor as I would my EXTERNAL Monitor. And consequently when I don't use as it this way it reverts back to being a 2nd or DUAL monitor.

And yes, check in your DISPLAY setup to see you have the option for extending the desktop to this second monitor - not an external monitor.

I've asked these question 'cos I want to know your setup and understand exactly what your problem is.

Grazie,
I did respond to goshep but it did not go through so I will state my situation again.

I am using an Acer laptop with a Mobility Radeon 9200 which has dual monitor capability. I have connected a computer monitor to this, and no other monitor, so I guess by your definition I have dual monitors. But today things have gotten even crazier. The second monitor is now showing my wallpaper, whereas yesterday it was showing the exact same screen as the laptop display. I must admit that I have clicked on many things since then and may have inadvertantly changed something somewhere.

It was many months ago that I first set up dual monitors and I had no problems then. Eveything worked OK first time, but I am having a Dickens of a time now. At that time the second monitor did show my wallpaper, as it now, and I could drag the Preview Window onto the second monitor. But it will not do that now.

I did try checking and unchecking the "Extend desktop to this monitor" box, as suggested by goshep, but that had no effect. I have gone all through the Display Settings I can find and the "Help" instructions, but nothing seems to work.

Any help would be appreciated.

Laptop.
You *have* toggled the 3-way settings (laptop only, both, external monitor only) with the Function + F5, right?

Something to consider is that some laptops cannot drive both LCD and external simultaneously when running Windows Media Player - you'll see the player, but not the image the player is playing. Simply not enough signal strength to drive both devices with both images. On my Averatec we have to toggle FUNC-F5 to "external only" to see the whole picture. So to speak.

David

Ron R-
I have a similar set-up and also have a Radeon adapter (9800 though). I've experienced the same thing as you, especially after having my laptop connected to an LCD projector. Here's how I fix it:
1. Make sure the second monitor is connected and power on, then right click on your desktop, select Properties, then select Settings.
2. Go to Advanced and in the Radeon properties, select the tab named Displays
3. In the Displays menu, make sure the Monitor icon has the "2" selected (as in your second monitor) and the Panel icon (your laptop) has the 1 selected (one, as in your first monitor). Selected means the little blue button is presed in. Also, make sure the upper-left corner of these icons is activated (pressed in and green). Select Apply and OK.
4. Back at the settings tab under your Display Properties, you should see two boxes representing your screens, one with a "1" and one with a "2"). Click on the one with the "2" and make sure to put a check in the box next to "extend my desktop onto this monitor".
5. Just to be sure all is well, click on the Identify button and you should see a "1" on your main screen and a "2" on your secondary monitor. Also, make sure you have these boxes representing your screens oriented the same as they are sitting on your desk- laptop on the left, 2nd monitor on the right (or vice-versa).
6. You should now see that screen #1 (your laptop) has your system tray, start button, etc on it and monitor #2 doesn't. If not, restart your machine and it should all reset properly to the Multiple Monitors layout.
7. One final comment- you mentioned that you can't move your Vegas video preview screen to the second monitor. Can you move the Vegas preview screen around on your primary monitor? This may be obvious since you've had the preview screen on the second monitor in the past, but in order to move the preview screen elsewhere, you need to position your mouse over the verticle dots in the top left corner of the preview screen (right below the "X" and the "<") and drag it to where you want it.
8. The toggle Fn + F5 advice is correct, too- it should be toggled to the Laptop Only setting, otherwise, you're sendng the same signal to the external monitor that you have on your laptop (and that's not what you want to be doing). That being said, once I have my machine in the Multiple Monitors mode, toggling Fn + F5 has no effect on the display.