|Did you update your video driver? Download the latest driver from NVidia.com for your system/card.|
Did you manage your programs that start with Windows? Run msconfig (start/run, type msconfig), go to Start tab and uncheck all except Microsoft items and your antivirus program, Apply and let it restart the machine. Try your game again. If later you find that you need something to start with Windows (like APC for your UPS, etc), you just launch msconfig again and check that program and apply.
Run Disk Clean Up (Computer, right click on C drive and select Properties, then choose Disk Clean up and check all boxes and proceed).
Run Malwarebytes scan in Safe Mode and remove all it finds.
What antivirus program are you running? Some like McAfee and Norton are known to bog down systems when there is really no reason to. Try MS Security Essentials (free), Avast (free version), or Webroot Secure Anywhere (my personal preference, but pay for) as all of these will use your systems resources sparingly when other programs need them and will only interfere when absolutely necessary.
You have to be a little bit crazy to keep you from going insane.