Reinstall as protection

Hi all;

This is my first thread in this forum and I'm not really sure if this is the right place for my questioning. It's a bit difficult because I feel exposed to be thought of as insanely paranoid, but there is 'something' about my pc that continuously leaves me with a feeling that I'm being watched and tampered with. The symptoms are adverse and .. as far as I understand PCs .. beyond virus and malware.
Years ago I bought a year's protection of Norton antivirus .. it never came up with anything, and I havn't spent money on it since. I've got into the habit of making a clean re-install of the system instead, and I do that on a regular basis.
1) wouldn't such a re-install wipe off anything malicious?
I do keep 'data' on drives that is not changed and I believe that I'm able to discern on what's data and whats executable.

On the previous re-install I followed up on going online to make the 100+ windows security updates .. and the very first thing was to activate another month of net-time. When my net-time expires, I'll be redirected to the providers pages when I go online. At the said session, I noticed that the first thing that happened was a 2mb (or 20) download before the redirection took me to the page. I got feedback from the provider, that their software does not update itself .. leaving a question of: 2) what can bypass my provider for download?

I've been meticulous about setting myself in charge of the windows downloads & install, and I'm not aware of giving permissions to other programs to act on their own.
Immediately after having been in contact with my provider on the problem, the next pc-session had one of those corrections of the register-settings that often happens after 'updates'. I had not initiated an update, so I found that suspicious.

At my re-install yesterday, I noticed that it spent longer time on setting itself up than usual. Paranoid as I am, I consider the nuisance to have moved to the pre-installed 'image' of the system that's being installed.

3) Is there anyway around this, than ditching my pc and start an aquarium nursery, a window-garden or doing cross-words?

I look forward to your responses.

Kindly CarstenT

Asus 64 bit pc & win7 home