high cpu usage

Firefox wanted to update but i already have the latest version.However i clicked on update but when the update finished firefox would not open.I looked in task manager and found norton was using 50% of cpu.I also tried to install malwarebytes but after download it too would not run.I tried  a few things and found if i rebooted and did not try the update for firefox everything was ok.I have now uninstalled  firefox and reinstalled and also uninstalled and reinstalled norton.I am using windows 7 64 bit and NIS 2011.

Is there a rookit kit scanner for windows 7 so check my laptop?All scans from malwarebytes and norton are clean.