Just a couple of ideas.
1. have a PPRuNE mail account as the email account set up in your profile here on PPRuNE. When I first signed-up here I used my regular AOL email addy and was (relatively speaking) bombarded with spam!
2. In Start-Settings-Control Panel-Internet Settings use the Delete History option on a daily basis and set Clear History to zero;
3. Regularly Scandisk/Defrag puter so that space is maintained in healthy fashion;
4. Regularly go to C

Windows and delete ALL contents of Temp Files and Temporary Internet Files.
With the circular "you cannot delete this" I can't help ...consider, however, getting a good virus-scan system (like McAfee's Clinic) and use it!!!
Hope this helps, even a little!
JC