Arduino's Overcurrent Defense Mechanism?

... and you measure CURRENT inline with the circuit path... not ACROSS the power leads. You placed very LOW low value resistance shunt across the power leads creating s short circuit on the 5V power feed from your PC. The PC is designed to sense these shorts and will disable the USB power.

This is a good way to fry the fuse in your meter as well, depending on settings (if you have a low current setting).

Note: the value you got from your meter, as stated already... is bogus.