That's really strange. As the others have said, the ground for the mobo is provided via the powersupply. You should be able to mount it on rubber without any problems 😉. Sounds like the ground wire from the powersupply is bad. Have you tried putting the ps back in the case and seeing if it still works there? I've never owned a bx6 (though I did have more than one bh6), so it may just be something really weird that Abit did with bx6, requiring that it be grounded to the case as well as the ps, but I don't see why that would be necessary. Ground is ground, and the ground wire from the ps should be more than sufficient unless you've accidentally severed a connecetion on the mobo, thereby forcing it to need a second source for its ground. It would still be weird regardless, and severing a ground connection alone would have to be hard to do.