Hi,

Hold off on transferring files yet, but if you are worried about losing them, put the files on a CD which is a more stable source to store on rather than a USB drive.
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Give ComboFix a little bit longer...your system was severely infected and it may take some time to finish. If it still has not finished in about 30 minutes or so, go ahead and stop it and reboot your system. If there is a log created post that. If you don't see a log created, check inside of C:\ComboFix.txt and see if that file was created. If it is there post that.