What kind of firmware are you running? I think in your other post you said Marlin but it was a custom version. Are you making sure the comport speed (baudrate) in firmware and the setting in Pronterface match?

Last week, I noticed that the USB connector on the master board of my printer was broken. I wasn't using the slave board at all, so I decided to do a switch of the masterboard and slave board to solve this problem. I switched the slave and made it the new masterboard, and the old masterboard now became the slave. (First of all, is it okay to do this? I'm operating on the assumption that the master and the slave are the same). And then I connected to the USB to the new masterboard, and the LED light was blinking as expected. But the printer did not connect, and I assumed this was because the firmware on the new masterboard was that of the slave. So I upgraded/uploaded the correct firmware onto the master and the slave.

Now I tried to connect the printer, and pronterface is still not recognizing the port for communication. The port shows up in 'Unknown devices' when I go to device manager on the computer, and I manually made sure that the port COM3 was recognized under 'Port', and even after I do this, I get an error message in pronterface saying cannot connect because access denied to the port.

Any ideas? Please help!