If you syncing will not start and is stuck on step 1 or 2 (backing up) try deleting your most recent backup by going to iTunes preferences, on the Devices tab click on your most recent backup and click Delete Backup. Then try syncing again.
The usb isn't the issue. If the iphone is being charged by the usb cable, we know the cable is good. The issue might have to do with security software that's been placed on the computer. Is the device being recognized at all in itunes?