Aha! Possibly your system came with a system restore partition that will restore your original settings, or settings at some earlier predetermined point. If so, you may want to try that software so it can reset the settings to a point the day before you installed the new version of XP.
Also, if you are brave, go to My Computer, and at the top go to Tools -> Folder Options -> View, and select the Show Hidden Files and Folders option. Also, uncheck the Hide protected operating system files option. This will let you see a lot more of what is on your drives, and may help explain a lot. While you are there, you should probably uncheck the Hide extensions block, as hidden extensions are one tool that folks use to sneak bad stuff on to computers.
When that is done, select OK, then pres Ctrl-R. Do you see anything different?
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