ive had it happen after installing ati catalyst control center. hate to tell you but norton isnt all its cracked up to be.ive found avast does a better job for free. try running malwarebytes.scan,get rid of anything it picks up and post a log.just to be sure download and run a scan with hijack this from trend micro.dont fix anything with hijack this yet,just post the scan.may be nothing but better safe than sorry.
http://sourceforge.net/projects/hjt/
http://www.malwarebytes.org/