Using RobotC, Modkit, or Robot Mesh? Graphical or text? On PC, Mac? Windows 7, 10, or Mac OS 10.x.x?
When you say “online interface”, do you mean VexOS Utility (firmware)? Did you successfully update the Utility to latest (2.1.3)? And no brain icon shows?
Or do you mean RobotC (latest is 4.5.6) won’t connect?
You might be helped by this (click the triangle):
drivers...
I have had one group of robots link to several Windows 7 laptops and not to several others. Another group of robots reversed that. It was when I was in the middle of Windows updates, and VexOS and RobotC and Modkit and Robot Mesh updates on 21 computers and 30 robots. The above quote helped me, and on occasion, switching to a different serial port on the laptop has triggered correct driver downloads.
Did you have both working before, and has something been changed since? Is the unresponsive brain normal otherwise; System Info and Devices Info?
He’s probably right, seems to (almost) always be.
PS, sometimes a different USB cord will work (temporarily) in a flakey USB port. And, this: