Do you get the chimes sound when you plug in the usb? If not, the usb cable may be bad (seems highly unlikely), or you could try another port. My wife's phone is a Motorola Droid3, and Win 7 auto-installed the drivers when the phone usb was plugged in. A background program called "MotoHelper Agent " can be seen running in the background in Task Manager Processes.....you might look for that. But her Droid 3 runs fine. If you want to pursue this, I'd be glad to help.
Tom