> Where do I go from here?  How do I determine whether I have faulty hardware
> (the 21041 and Mach32 were functional before, but board and memory are new)
> or whether I have a configuration/installation problem?  Should I try this
> with a serial console instead (I really don't need a graphic console)?

Yes, you should. Either the problem will go away or you will be in a
better position to extract information on it. There are recently added
ramblings on the subject of serial consoles in the FAQ.