3 beeps, then repeat every 5 seconds, should be related to RAM. Remove the RAM, then insert only one stick.
Be careful that it is fully seated.
If you still get beeps with only one stick, move THAT stick to the other slot, then try the boot again.
Repeat the same process with the other RAM stick.
No change? Try different RAM.
Also, something that I would try - replace the battery (should be a BR2032). It's on the back side of the logic board, which has to be removed to get at that battery.