external display issue on Dell D610

The dual and external display functions (Fn - F8 positions 2 and 3) which had worked for at least two years, suddenly stopped working on my Dell D610 (unfortunately my main work laptop used for presentations in boardrooms).  I have tried everything I can think of - display settings, driver updates, adapter conflict checks, the MS windows troubleshooting wizard, etc.  I know my external display devices work with other laptops.

Occasionally, while I was changing display settings during troubleshooting the external device displays the desktop background without anything else so there is some signal being sent to the external device sometimes.  Most of the time the screen is just black and a "no signal" error message is reported by the display device.

Before I go through the pain of ditching this machine (which has been fine in most every other way) does anyone have any ideas?  I'm getting too old to change too frequently or without a very good reason.

Thanks.

Specs are:

OS System:  MS XP Professional Version 2002, Service Pack 3

Dell D610 Intel Pentium M 1.73GHz, 504 MB RAM