First of all, you shouldn't be running Combofix on your own.
volsnap.sys file is one of the main target of TDL rootkit.
Disinfection and removal requires some guided help.
Playing with volsnap.sys file may make your computer unbootable.
With the information you have provided I believe you will need help from the malware removal team. I would like you to start a new thread and post a DDS log HERE
and include a link to this thread. Please make sure that you read the information about getting started
before you start your thread.
It would be helpful if you post a note here once you have completed the steps in the guide and have started your topic in malware removal. Good luck and be patient. Help is on the way!