Display Driver Crash on Optiplex 5040 using Excel

We have 3 new Dell Optiplex 5040's ( i7, 8GB Ram, 500 GB HDD) with no addon gpu.  On all the computers the display driver randomly crashes and recovers while using Excel 2010.  I have updated to the latest display drivers, turned off hardware acceleration in Excel and extended the display driver timeout in the registry.  The registry fix made it longer between crashes but did not fix the problem.  Any suggestions?