If when you are trying to back up your Windows Phone 7, you find that the Zune software has stopped responding, then you may have to check and ensure that the Windows Mobile Device Updater is up to date.
Zune software freezes
You will have to update the Windows Mobile Device Updater (ZuneWmdu.dll) component of the Zune software to version 4.7.1407.0 or later versions.
You can download and save the Zune4.7_update package from KB2498092. It is a .zip file which contains both 32-bit and 64-bit versions of the Zune software.
Or you can download and apply Microsoft Fix it 50525 and let it fix it for you!
Hope it helps!