Welcome to the SeeMeCNC Community

It use to work: I printed the fan shroud successfully.

But today, it won't connect from my laptop to the printer.

So I remove the printer profile, created a new one, get to the "Attempting to Connect" step, and it stops there.

Rambo board has a single green LED, not sure if there is any other diagnostics to make sure it is ok.

I've tried a cold reboot of everything.

OSX: MatterControl Build 1.5.0.6722

Have you tried using another USB port on your computer? Is the computer seeing the device at all?

I've had this problem. Sometimes, after restarting your mac, the usb port the printer is plugged into gets mapped to a different com port. Edit the printer profile and select the available port, (not at my mac right now so I can't give sample port path). I get this 2 out of 3 times I restart my mac. I don't seem to have that problem when I just sleep it.