Having issues with new MendelMax 1.5 build

Hi!
I just finished my MendelMax 1.5 build. I uploaded the Marlin firmware, and the X-axis seems to work ok, but Y-axis is very jerky. It'll move a few inches, then the motor will sound like it's grinding but it's actually not moving. It kind of moves but very choppy. The Z axis does nothing but hums when I try to move it using Repetier-Host but doesn't even budge. I tried turning the potentiometer all the way up (clockwise) on my power supply. I'm using everything that came with the kit. I can't think of what else to try. I've never gotten it working past this point before. I tried other firmwares including Sprinter, but after uploading it, I can connect to it using Repetier-Host but absolutely nothing responds. Can't move the motors nor heat up anything. I've tried the test code, and my X, Y and E motors all seem to move back and forth (E seems to be choppy and jitter as it spins. But Z doesn't do anything. I'm not sure if it's supposed to move using the test code or not.
My PSU is 12V / 29A. I'm using RAMPS 1.4 with Arduino Mega 2560. It almost seems like the motors aren't receiving enough juice.
Please help!

Motor current is set by the pots on the stepper driver chips.

Do you know what the current specs are on your motors? If so, grab a DVM and see how the Vref on the drivers compares to the proper Vref for your motors. I'd try setting things to 1/2 the rated current and see what that does for you.

lets share info. I am having issues with merlin, complier errors
you problem I believe is that your motors can run that fast at that current. try first to lower the x,y,z feed rate real slow say 10 mm / sec
then move the motors, you should not be able to stop the motors by hand, if you can turn up the power.
the motors will make noise but will be strong. Mine is ok now.
Don't worry about steps etc, unless you have them calibrated, at this point.
tech guy

If the motors he has are 5A 0.5V motors, he could easily max out (and maybe fry ...) the driver boards before he gets things set up. Best to know what the motors are set up for before you start fiddling things....

My apologies, I solved this issue ages ago but have been excitedly working on it and forgot to respond
You're right, It was just that I hadn't increased the voltage on the potentiometer on each individual motor driver on the RAMPS board. They send them with the lowest setting, so I increased them to the recommended voltage based on their documentation. Working like a charm now.
Thanks very much for your responses!