Each license will only work with the PC where the license PC ID came from, but you can have 5 licenses. Just go get another license with the PC ID from your nicer computer!! You can deactivate a license, too, if, perhaps, in the future you get an even BETTER PC and get rid of one.
If a PC dies, get a new one, install Mach, get a license, copy your entire Mach4Hobby directory over, done. Go deactivate the old PC license on the web site. If you somehow run out of licenses, contact Artsoft, they're pretty good to us Hobby guys, they're not trying to hobble us, they're trying to stop the real bad guys.