I did not configure any bios setting or anything to my motherboard beforehand.
so today , my motherboard suddenly couldn't detect my GPU(R9 290 Tri-x sapphire) and i tried to use the cmos jumper to reset the bios .

it worked but .... my hashrate was originaly stable at 30Mh/s(on ethereum) and now it is only performing at 27Mh/s

Does anyone know what is happenning? thanks!