Open up your task manager an make sure you see all cores/threads there in cpu useage. Most likely you will see missing cores/threads, what you need to do is open msconfig select the boot tab, click advanced options, and uncheck number of processors and hit ok.
Greeting.. i run same problem week ago, i fix it by Install/Running CCleaner . make sure you uninstall 3Dmark13/11 then restart window 8/7 then install Reg cleaner software CCleaner then install again the 3Dmark13/11 .
Other way fix is/ Fresh re-install window8/7
Course of this issues is Registry DLL created by 3Dmark13/11 (usually happen when user Frequently Benchmark Trial edition)