Test your HD using maker's full CD scan: Hard Drive Diagnostics Tools and Utilities (Storage) - TACKtech Corp.
Test your memory using Windows Memory Diagnostic test for two passes.
After factory recovery, remove Norton bloatware infection with the free Revo Uninstaller in Advanced mode, then follow up immediately with Norton Removal tool to check for any remaining infection. Install Microsoft Security Essentials in 30 seconds for lightweight, invisible, unintrusive free AV.
Continue using Revo Uninstaller in Advanced mode to clean uninstall any other bloatware programs you don't want.
Do your updates, paying close attention to newer Windows 7 drivers given in Optional Updates.
After it is set up and running as you like, type msconfig in Start Search box and remove all freeloaders from your RAM/CPU by unchecking any programs that don't absolutely have to startup with computer. The only ones I allow are AV and Sidebar (gadgets).
Finally, use state-of-the-art free CCleaner "Run Cleaner" and Registry tab, then free Auslogics Disk and Registry defraggers to keep HD perfectly clean and ordered.
When its all done, get a Windows 7 backup image stored externally so you never have to reinstall again, just reimage using Repair CD in 20 minutes.