It could have to do with you're plugins in mach, Try removing all but the one you need to run mach then run it and see if it still happens. If it doesn't then put each plugin back into the plugin folder until you find the offending one.

It might not be the issue but I have had some computers crash mach due to a plugin soaking up to much CPU time, never BSoD but it's worth a try.

Dang! I found two bad capacitors on the motherboard... I am going to replace them and let you know.

If that does turn out to be the problem I will be shocked due to the computer only crashing under Mach.

It could just be Mach is puting extra load on the computer compared to other programmes you are running, heres hoping you have found the problem.
Hood