Monicaxo, when windows freeze while copying files means that there is a bottleneck somewhere in the system. Can be a wrong driver that control the USB storage, can be a faulty usb port (you may try a different usb port) or can be "simply" a corrupted windows 7 installation.
There are many ways to backup contents to your computer:
1) Via USB and Xperia XC
2) Do a backup in your SD card, then connect your SD card to your computer using a SD card reader
3) Bluetooth connection: transfer files to your computer using Bluetooth
4) Copy the content of your phone using Google drive or Dropbox or One drive or whatever cloud storage service you fill comfortable and then download the content in your computer.
Now, question: what are the specs of your computer? Does it have usb v.2? Is it a laptop or desktop?