Active window disappears momentarily

When in either Outlook or a browser window, and inputting information into a field, the active window disappears momentarily exposing the desktop to view. It still takes all keystrokes in the background, the subject window is still active because any keyboarding is reflected when the window reappears a few seconds (5-10) later. It seems to take down all open windows.

Running Windows 7 Pro 32, on a Lenovo T400 laptop - Core 2 Duo P8800, 3GB PC3-8500, 160GB-7200rpm, ATI Mobility Radeon 3470 with 256MB connected to a ThinkPad Essentail Port Replicator. Resolution - dropped to 1024x768

Disconnect the port replicator. Does that fix it?

Will try that, although with the laptop open while attached to the port replicator, both screens behave identically. Will let you know.

So far so good, no problems without port replicator.....will contact Lenovo for answer as to what gives ..thanks

This is happening on my new desktop Dell Inspiron 560. Running Wndows 7 Home Premium 64 bit w/Firefox. I did just download driver updates. Would this cause the problem? Any help would be greatly appreciated.