Sounds like you may need to download a custom screen. If you have already got that from Bobs site then you will have to make sure you have it placed in the Mach3 folder. You will probably also get bitmaps with the screen, you will need to place them in the correct directory which will more than likely be C:\Mach3\Bitmaps.
Once you have done that when you start Mach again it should be ok.
Hood