i have a similar problem
the first time i plugged in my lumia 920, it popped right up and i got some music on there, and today i wanted to throw some more on. however, i tried with two win 7 64-bit PC's and neither of them found my lumia, but it was still charging...is there a fix yet?
Sorry MaulerX, but that's quite possibly the worst reason to update. What if he spends 40 bucks just to find out there is another problem that's causing his issue?
Windows 7 is still supported and will/should receive attention from Microsoft which is why they released this tool to begin with, this is not Windows 98 SE.
I'm still upset that I was forced to update to Windows 8 to install the developer tools for Windows Phone. Then I come to find out later that Microsoft will not be supporting older Media Center extenders on Windows 8.