Chosen Solution
my macbook pro mid 2012 15.4 does not start and beeps 3 times at statup
3 beeps = bad RAM or incorrect RAM. Please give us the last three figures of your serial number for the correct RAM type.
I have the same issue as well with a MBP Mid-2012 model Intel Core i7 2.9GHz with 2 4GB RAM. Sometime the screen will glitch and I will see artifacts on the screen. Other time it will suddenly shut down and then beep 3 times when I try to turn it back on. Usually I have to open the back cover take out the battery and reinstall the RAM for it to turn on again. I recently noticed that if I apply pressure on the bottom of the laptop or if I move it will start having problems. I tested it with one RAM in the top slot and it is now working fine. I moved it, applied pressure, tried having multiple applications open and it did not give me any problems. Hopefully this fixes your issue.
I’m having the same issue as enrique, but only using one RAM slot and not moving it around is not a solution.
