I'm thinking I had similar problems when I installed the SP2 beta.
I'd consider using the system restore to a date prior to the problems.
I'd do everything stated in the link franktiii gave ya.
Clean out your temporary files.
Clean out your temporary internet files.
Regarding those applications to download, update and install...Run 'em
. All of 'em Reboot several times.
Personally I'd install AVG free anti-virus and set the Norton 2006 aside,
(uninstall it temporarily) and use it again later perhaps.
I'd also download Ewido anti-malware and use it, toohttp://www.ewido.net/en/
and A-squared, for that matter, also:http://www.emsisoft.com/en/software/free/
Visit those online scans, observe the behavior while there.Practice using the safe mode
instead of normal mode when you do all that stuff.
Just remember no online connection will be available in safe mode,
but installs/running applications will work,
and even better since fewer drivers are running and that makes it easier for those applications to be effective at times.
So, do those things B4 posting, please.
It will be to your advantage.
After posting do very little to change anything and exercise patience.
(Ask questions about this advice as a reply here if you like)
a reformat might sound easier
but you'll need to know what to do in the future, anyway.