Dual screen monitor - wrong resolution options

I have a Dell Latitude E6420 running Windows 7 Professional 64 bit which I use at multiple workstations in various locations.  Most have docking stations connected to one or two monitors (one VGA, one DVI).  I run dual screen as often as I can, so even at a workstation with only one monitor, I will use the built-in screen as a second monitor.  I also have to give presentations from my laptop, usually through a VGA connection to the laptop's port.

There is one particular meeting room which has two plasma screens in it which are driven from one VGA connection (so always display the same output and show up as only one monitor when connected to the laptop).  I use this room a lot.  Until recently, whenever I plugged in there the monitors would show a full-screen image at a regular resolution (800x600 or 1024x768).  I use these monitors as secondary, with my laptop screen as primary.  I control all monitor activity through the Intel(R) HD 3000 graphics driver interface.  The driver is the latest available from Dell (9.17.10.3040).

However, now when I plug in at this room, the secondary monitors show a squeezed image (in the horizontal axis) and the only resolution options offered by the driver are 1366x768 and 4x3.  Yes, FOUR by THREE pixels.  Neither of these are the native resolution (which should be 1024x768).  Nothing I can do will get the monitors to show full-screen at the right resolution.  My colleague, with (nominally) the same laptop, has no issues.

There appears also to be some kind of cache, or memory for monitor configurations.  Whenever I drop down at a workstation, Windows automatically sets up the monitors in the way they were last time I was there (so with the monitors in the correct relative locations, resolutions etc).  Is there any way of resetting this memory, so that I can start afresh?