which dll do you have the video out set to under preferances gxl2bas32, Gxl2DX8A or Gxl2DX8? you may have to change it. also be sure your Direct X is updated as well as video card driver

make sure your not running or do run any other DX application while MED is running ( especialy running WED and MED at the same time) can causeone, both to crash or DX rendering to fail completly