This is one of the reasons why we recommend not to use ComboFix on your own. There are risks involved and we would prefer it if someone who knows how to resovle any issues that may arise is supervising its use.
ComboFix disconnects the computer from the Internet as part of its routine. If you did not disconnect, you may loose your connection. The connection is automatically restored before ComboFix completes its run. However, if ComboFix runs into difficulty and terminates prematurely, the connection can be restored by restarting your machine again.
If rebooting did not restore your Network and Internet Connection, then follow these instructions for Manually restoring the Internet connection