Samsung Galaxy S3 not detected

I've been looking all over the internet for a solution to my problem, but nothing seems to work.

I have my Samsung Galaxy S3 device connected to my PC. I've tried everything using several different USB ports. My goal is to have Unity detect the device, so I can build directly to it.

On my laptop I have no issues. I can safely build to my android device without any errors. On my PC, however, Unity tells me it cannot find any Android devices.

Everything I need in the Android SDK Manager is up to date. My device is set to debugging, and MTP mode. But when I use the command 'adb devices', nothing shows. I've tried 'adb kill-server' and 'adb start-server' countless times, to no success.

I've tried using USBDeview to get rid of all the USB drivers on my PC related to Google or Android, so it can all get a fresh install, but no success here either.

I suspect that the problem has something to do with the device being recognized as a 'Portable Device', specifically, a 'GT-I9300'. Before, it read as a 'MTP MultiMedia Device'. Several online help forum posts and tutorials mention that the device should be listed as an Android Device in the Windows Device Manager, but this just doesn't happen.

I suspect I need to install my own custom drivers onto the device, and not let Windows install it's own standard MTP Drivers. But how do I do this?