Hi

I can see you've already tried quite a few of the things I would have suggested.

I can confirm that the HD500 drivers do load and work successfully under Windows Vista 64 bit as one of my machines does run that OS (the Ultimate version) with no issues with any Line 6 devices.

I think ideally you need to rule out the possibility that your HD500 doesn't have a hardware issue here by installing the drivers etc... on another computer - maybe an older one which runs XP - and ensuring that it does work correctly.  I am fairly certain it will be fine and that the problem will reside with your PC's configuration.  The fact that Device Manager is detecting the HD500 as an unknown device points to that probably being the case.  It would appear that Windows cannot detect the device driver correctly for some reason.

Here's what I would do:

I would ensure that Windows is fully up to date with the latest service pack (should be SP2 now).

I would start the system in Safe mode and take a look at all the entries in Device Manager and delete any devices that are no longer relevant or devices that are maybe listed as the HD500

Whilst still in safe mode, I would find the folder called INF in the Windows directory and delete anything applicable to the HD500 - you may have to dig to find the correct .inf files, but if you sort by Date Modified (not Date Created) it should be one of the more recent files - you can open it in NotePad and read the contents - make a note of any driver files and destination locations listed too so you can manually delete these whilst in safe mode.

Delete or preferably rename the INF file by changing its file extension from .inf to .in_ so that Windows won't simply re-use it to reinstall drivers incorrectly again.

Delete the actual driver files as listed in the INF file.

Restart Windows with the HD500 disconnected

Download the HD500 driver files directly from the Downloads section for your version of Windows and install them by running the .EXE file.  Only plug the HD500 in when directed to do so

Once the drivers are installed, download the latest version of Line 6 Monkey and run it.  This should detect the HD500 and it will probably show that the HD500 can be upgraded to firmware version 1.31 plus the latest version of HD500 Edit should be listed as well.

If that doesn't work, but you know your HD500 itself is OK because it works on another system, then I would use the other system to update the HD500's firmware and then re-connect to your system.  This shouldn't actually make a lot of difference to how your system detects the HD500 because it should work whatever, but there is a small chance that the combination of Vista 64, an old firmware installation plus the latest driver may not see eye to eye - I should mention too that in the Downloads section of the Line 6 Web site you will find older drivers listed for the HD500 which is something else you could try.

I doubt whether this is the case, but there is a small possibility that the USB hardware in your system has some kind of compatibility issue with the HD500, so maybe an inexpensive USB 2.0 card might be the answer.

Nick