HDMI no signal after moving ram?

i just got this pc off my brother, it was working perfectly until i tried to fix the slight ram problem, i have 16gb in it and it was only picking up 8gb, so i turned it off, unplugged it, unlatched the ram and carefully removed then reinstalled it.

then, all of a sudden, it gives no hdmi signal, i've tried moving the ram around, i removed and moved the graphics card to a different slot, i've tried different hdmi cables and nothing seems to be working.

can anyone help?