Computer boot but no sound, no image on mntor

Hello,
while i was playing with my computer it lagged a bit then i heard a weird beep sound. so i opened up my PC and i cleaned my ram with an eraser then i changed it to another slot but this time it did not beep instead it boot but their was no image from the monitor i thought the graphics card was broken but its fan was working

please help....!
SPEC:
n-force 3-A
512MB RAM
40GB HDD
GEFORCE SERIES (DON'T NO WHAT)