PC turns on but screen blank, beeps 3 times at regular intervals

Yesterday my PC just turned off and won't turn on again. When I try power it on, I get 3 beeps (which keeps going at regular intervals), and nothing displayed on screen.
I've tried the following already:

Removing RAM, removing video card and placing them back in. Nothing changed, I keep getting the beeps. I know the PC is turning on since I hear the hard disk booting.

The specs of my PC:
MB - Asus P5VD2-X
4 GB RAM
550W PSU
Asus graphic card
 
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