Measured resistance on GND inputs? (for 11a and 5a) (no replies)

I've had some issues with my new, never used Mega 2560 r3 + Ramps 1.4 combo. The Mega 2560 died and I'm not sure why.

Ramsp was stacked on Mega. I connected 12V inputs to ramps and then USB to Mega. Mega didn't show up on my PC - it did a few minutes earlier without the Ramps.
I had nothing connected to the Ramps 1.4 except both input powerlines which I triple checked many times.

I've tried googling and searching here and other Places but fault-finding hints are few and far between.

I found only two things to measure on:
I read I could measure from each input Vcc + the fuses and it should read 12v - it did.
I can read voltage on D8 when power is connected.

One thing I'm not sure about is that I can measure about 6ohm resistance between the two GND inputs when nothing is connected to it. Is that normal or does it indicate a short?

The Ramps board does not smell burned and there are no visible indications that anything is faulty.

I hope a new Mega 2560 arrive tonight but am vary of attaching it to the Ramps...