You can take a look at your current bandwidth usage on Windows easily using the Resource Monitor.

If you click on the Start button and type: resource monitor it should come up as an option. Alternatively in the Run box type: perfmon /res

This will open your resource monitor.

Click on the 'Network' tab

Then click on the white square box to the left of a service that is using a lot of bytes (note that VPSBlocks only tracks Bytes Sent so look in the 'Send (B/sec)' column.

You can also click on 'System' which usually gives you a good idea of what hosts you are connected to.

Using this information you can determine what is using your bandwidth, you can stop the associated service, or block IPs/Addresses in your firewall.