If you've already downloaded and tried to install the latest driver from the Line 6 website, but the pod is still considered unknown by the computer then try this:
Have your device (pod or whatever) unplugged then go to your Device Manager. Plug in the pod. You should see a new device pop up under the "Other devices" tab... and it should be labeled simply as "Unknown". This is your pod. Right click it and choose "Update Driver Software". Choose to browse your computer for the driver software. I had trouble with Windows 8 finding the driver even if I pointed it directly to the correct folder ("C:\Program Files (x86)\Line6\Tools\Driver Archive\POD HD 300" for me.) So I chose the "Let me pick from a list of device drivers on my computer" option below that.
I then searched in the "Sound, video and game controllers" option for the hardware type, which brought up "Line 6" as a manufacturer option on the next page. I then selected that and my appropriate driver (Pod HD300 for me.) Windows briefly complained about unrecognized certificates or some such, at which point I said continue anyways. A driver installing progress bar then started. Strangely enough the progress bar seemed to get stuck (which shouldn't happen, this driver is small and should install pretty fast), but I let it run for about 5 minutes and then killed the process from task manager (just trying to exit the window doesn't work because Windows complains about you stopping a driver install before it's done... as it rightfully should, but the Line 6 software/drivers are just so buggy and hard to get going I had to go to drastic measures.) After that it seemed fine; when I relaunch device manager the pod shows up as a recognized device under "Sound, video and game controllers."
Note that you may have to repeat this process for other USB ports if you plug into a different one next time, so maybe just try to be consistent about which one you use.
These instructions are what I did on Windows 8.1, but they should be valid for Windows 7 as well. I'm not sure about Vista, perhaps. Also note that the last step is pretty sketchy... so standard disclaimer: I'm not guaranteeing it will work on your own personal system, or even leave the system in tact, this is just what I had to do on my own computer.
