Recheck your work and verify all is well, DON"T TAKE ANYTHING FOR GRANTED. I suppose the new mtrbd. is tested, OK as in verified. Next, if no cause is found for problem, you *may* want to remove mtrbd. and place on cardboard. remove other items to rebuild the PC outside of case and thus remove any shorts, or possible faults and be able to quickly check&inspect items or replace them. If it works that way, then return to inside of PC case and retest then. Use other cabling if possible and ordinate properly. Closely inspect cabling too for any cuts or indents that maybe a open wire or uncrimped pin, bent pins, etc.. GX270 don't take kindly to be opened, etc., as the tight quarters may "pinch" cabling, so inspect closely. Come back with results.

tada ------Willy Happy