See page 4 of the quick start guide for your monitor linked here. This monitor should install and operate with Plug and Play, drivers are native to Windows. See page 4 for navigating to the driver. Regarding the adapter, what did you do?  The adapter is your video controller, not monitor. If you attempted to load another driver than you have likely lost the video driver. Go to the Display properties (right click in the open on your desktop, select properties, select settings tab, then the advanced button). Select the adapter tab, click on properties button, select driver tab, check whether it is showing the dedicated driver installed or a default windows safe driver. If the latter, see if by clicking on 'roll back driver' button you can't maybe restore the display adapter or video card driver. If not, you will need to re install the driver for your integrated video controller or AGP card (depending on your options). The driver will be with your resource CD's, or can be downloaded from Dell Downloads, go to download tab above, if registered, then enter your system tag, select drivers, and find your hardware there, and download the appropriate driver. 

http://www.ita.sel.sony.com/support/displays/legacy/SDM_man/SDMHS_QS.PDF

Reinstalling the controller driver did the trick.  Thanks for your prompt reply.

Thanks,

AP