This webpage has all beep and no beep symptoms:
https://support.lenovo.com/pt/pt/docu...
The error found in this video (one long and two short beeps, and a blank or unreadable LCD) corresponds to: 1. System board, 2. LCD assembly or 3. DIMM.
To test DIMM (RAM) try booting your laptop with one RAM stick (or a RAM stick from another PC) at a time, as the probability of both sticks fail at the same time is very low.
If you still get the beeps try connecting an external monitor to your laptop (as the problem may be the LCD assembly).
If the beeps still persist, the problems in your System board (it will have to be replaced) and a new one will cost at least 500$...
The system board was the problem of my laptop. But, fortunately, it still was under warranty so it cost me nothing.
Good luck.
Note: your hard drive contents remain intact. That's good news... :)