Yep, did many cold reboots and quite a lot more but I was trying to keep the message short!
I've now removed both HD's and RAM and still no luck. I can still boot from floppy, put files on the HD and list these with DIR or TYPE. Trying to run any EXE file almost always results in a lockup - they never finish.
I'm still puzzled as to why I can use DIR, MEM, TYPE, CHKDSK and a load of other commands quite happily but the thing falls over whenever I try to run most programs. It does not seem logical to me that (for example) a DOS game can run, which means the systems are working, but Windows setup caused a lock. The only factor I can think of right now is file size and that it doesn't like big ones - but I'll admit I am looking for any sort of clue here as I can't understand the nature of the problem.
I still get an occasional "Program caused a Divide Overflow Error" but is this valid for a file like Scandisk?
With memory and HD both replaced that only leaves the mobo to check but can anything on it cause such weird problems? The BIOS appears to be working OK as I've reset HD values several times when swapping these around.
As you can guess I am really puzzled...