I think I may have fried the USB to TTL cable. The program that's on the MCU by default works, but when I try to connect to the device it doesn't work. The device is on, pin 14 is grounded, and the LCD shows blocks on lines 1 and 3, but /dev/ttyUSB0 isn't created and dmesg shows something like this:

[ 3934.090869] usb 1-5.4: new full speed USB device using ehci_hcd and address 36
[ 3934.174243] usb 1-5.4: device descriptor read/64, error -32
[ 3934.364089] usb 1-5.4: device descriptor read/64, error -32
[ 3934.550823] usb 1-5.4: new full speed USB device using ehci_hcd and address 37
[ 3934.634305] usb 1-5.4: device descriptor read/64, error -32
[ 3934.824036] usb 1-5.4: device descriptor read/64, error -32
[ 3935.010882] usb 1-5.4: new full speed USB device using ehci_hcd and address 38
[ 3935.433373] usb 1-5.4: device not accepting address 38, error -32
[ 3935.514071] usb 1-5.4: new full speed USB device using ehci_hcd and address 39
[ 3935.930107] usb 1-5.4: device not accepting address 39, error -32
[ 3935.930367] hub 1-5:1.0: unable to enumerate USB device on port 4

Is there some way I can test if the thing is fried? (I've also tried without the hub, which you may have noticed in the dmesg output).

What happens if you completely disconnect the wires from the board, and plug it into your computer, do you get the same thing?

If you connect the yellow and green wires together, you'll get it to loopback (IMPORTANT!! Do not short the black and red wires together, leave them unconnected the entire time) and if you load up minicom or something similar you can see if it feeds the letters you type back to you.

Also, why do you think it's shot, other then this? Was it working previously? Is this a new kit?

It worked at one point. I haven't used it for a while and now it doesn't seem to work anymore.

Plugging it in without the board gives the same messages in dmesg. Since no device node is created, I can't use minicom to communicate with the cable in the loopback configuration.

I also tried it on another computer with the same results (without the board connected). Also tried using Windows, and it couldn't identify the device or anything.

I just wonder... is the driver still installed?

Yeah, even if I explicitly modprobe pl2303 before plugging in the device the same thing happens. I guess I'll just order a new cable.