Difficulty in connecting to the internet

[Dancer]

I have not been using my Acer 5920 using Vista SP2 for quite a while as it is so slow and frustrating. I had trimmed my XP PCs and Xp Laptop by uninstalling programmes which I have not used for some time using Revo Uninstaller. Cleaned the registry using Eusing Registry Cleaner, ran CCleaner and defragged the Hard Drives. The Xp machines are a lot snappier now. I thought that I would try the same on my Vista Laptop. When I switched it on Microsoft Security Essentials kicked in requesting updates and suggested a Full scan. After this I had difficulty in connecting to the Internet, I tried Internet Explorer, Google Chrome and Mozilla Firefox. All of the browsers could not connect for one reason or another.
I am thinking of reinstalling Vista, but my machine came pre-installed without any CDs, not even recovery CDs unlike the Xp machines.
I assume that there must be a recovery programme on the hard drive somewhere. I would like to refresh the Operating System somehow. Is this possible the laptop is three years old. I have upgraded the RAM to 4GB and am thinking of maybe upgrading to Windows 7 if there is no other way to improve Vista's performance. Any Suggestions?
Best Wishes
Brian