Ram upgrade

My boss gives me an old Mac Mini (Mid 2011 version)

It comes with 1x 2G ram, so I purchased 2x 4G ram to upgrade it.

However, when I plug both 4G ram in it and power on, it has bi bi sound and no display.

It works when just use 1x 4G ram, I realized the upper ram slot is not working no matter I put the original 2G ram...

I brought it to Genius bar and they said the motherboard need to be replace and it cost HKD 3000 (USD 386)... I refuse to fix it...

Really disappointed on this issue...