I'm able to connect to Arduino+RAMPS through USB. I can even check end stops with `M119`. However, if I plug it to the power supply, my MacBook goes crazy and restart itself! Things I have tried:

- Uninstalled OSX, installed Ubuntu, I get readiness error when PSU is connected.
- Bought a new pair of RAMPS + Arduino.
- Run RAMPS all naked without anything on it.
- Measured PSU output, 12.2 V is stable.

I'm at a point I started to think my MacBook's USB ports are messed up. It is a 2008 model, do you think that would be right to blame?

**Update**

Tried a new and a very short USB cable: It worked for the first time, but laptop's trackpad gets very hard to control for some reason. Looks like I have to connect an external mouse.