Screen flickers and powers off,and gives 3 beeps when it's powered on

Hi,

i have this used MBP which used to restart every now and then.

Got it to the apple store they replaced the Logic board, RAM and thought it fixed the issue.

When i got it back after a day it started powering off all by itself and sometimes the screen flickers.

when i try to power it back on. i hear three continuous beeps over and over.

Tried upgrading the ram thinking that the new RAM's are faulty and i just wanned a 8GB instead of 4GB. But then it was still the same.

either it gives me the beeps or there's no display. i can just see the power light in front of the Mac on.

Please help me out.