The first thing I would do is completely uninstall anything that says Norton or Symantec. It's a
major resource hog. Follow the steps in this post, and we'll replace it with something equally effective and less demanding.
Next, run
Malwarebyte's Antimalware in
Safe Mode with Networking and remove anything it finds.
After that, download and install
Piriform CCleaner. Run the program, and on the left hand side select Registry. Scan and Fix Issues. Continue scanning for/repairing issues until it doesn't find anymore.
Then, if you're like 90% of Windows users, you probably have a
ton of extra programs starting up automatically when Windows starts up. You can disable unneeded processes from starting up by doing the following:
Go to Start-->Run-->type in 'msconfig' and hit <enter>
In the Startup tab, uncheck
everything that you do not need running in the background at startup and click "Apply." Then, in the Services tab,
check Hide All Microsoft
Services, uncheck
everything that you do not need running in the background at startup and click "Apply." Restart the computer.
Next, download and run the executable for
TrendMicro HijackThis!.
Press the button labeled "Open the Misc Tools Section". Then check both the check boxes next to the "Generate StartupList Log" button and click the button. Click the button to generate the list, save it and upload it as an attachment to your next post, and I or some other forum member will advise you on what else to disable, if anything.
Then run HijackThis! in normal mode and post your scan log here and we'll see if there's anything else that needs to be looked at.
Finally, you can install a free anti-virus to help keep you protected (these aren't nearly as taxing on your memory as Norton). I prefer
AVG Free Edition, but I've heard good things about
Microsoft Security Essentials as well.
Avira AntiVir and
Avast! are two more options. Please install
one of these programs to help keep you virus free.
After you've done all of these things, please wait until the computer is idle (no programs loading/scanning/etc), and hit ctrl+alt+delete and make note of your CPU usage at the bottom of the popup window.
On your next post, please include both the HijackThis! Logs I've requested, your idle CPU usage, any steps you left out, the make/model of your computer, and let us know how your it is running now.
Good Luck!