After pulling some hair out I've come up with this procedure and it is 3 for 3 so far with Win7 users having problem getting into an ADB shell.
navigate to C>Windows>System32>Drivers
Look for a file called usbstor.sys
You need to delete this file. If you need helping with permissions, let me know. I don't know how much you know about windows.
After deleting this file turn the phone off and boot into recovery.
Connect and 'click out' the SD card.
In CMD prompt run the loop file.
Click the power button and wait 10 seconds.
Volume down then power button....
Just after the white HTC screen you will hear your computer beep for an un-detect presumably for the SD click the SD back in as soon as you hear that sound. My Win7 realized the old drivers were no longer there and decided to use the ones we need.
After this process just follow the 'root in 10 minutes' video that mejdam posted and you should be good.
Let me know how it goes. Oh and worse case, if you're concerned with deleting system files, Windows will re-find it after we're done.