...and it was nothing to do with me, honest guv.
I believe you. No, really. It just happens. One of those death, taxes & my Windows PC is all messed up things. Now many people will try to sell or recommend so-called "registry cleaner" softwares designed to sort out the mess that your windows registry has no doubt become. That's all fine & dandy BUT for my twopeneth worth, the registry is just too complex a beastie for a piece of software to sort it out without guidance from someone who has a degree of knowledge concerning the windows registry. For the lay-person I would stay clear, these progs are a recipe for disaster. A much more effective course of action is to backup all your files & settings & just reinstall windows from scratch AND THEN put in place some measures to help keep your system in it's nice new pristine state (oh yeah, I hear you cry, ezi bleedin' peazy). All too often these days I see people just write off their "registry-mangled" PC as the result of "not being the latest processor) & just buying a new PC. Which is great until the same thing happens all over again. If you've got money to burn, fine, get your coat. if, on the other hand you'd rather spend your precious cash-money on other things (food, clothes, chocolate, a night out, botox, plastic surgery or whatever) then have a look-see & help yourself. I'm at the other end of an email, instant message or phone, should you need personal help too.
So, your Pee cee is just treacle city, slower than it was when new, slow to start-up, as sluggish as a slug at a "who's the laziest slug" contest. Before we can use our beige boxen for fun & meaningful stuff, we need to start with a clean sheet.
So...

• Use file, settings & transfer wizard to backup all your files & settings
• Use this guide
  
• save this file onto a secondary or external drive or DVD
  
• Reinstall your copy of windows XP (ideally allow it to format your hard drive)
• When installed, use Windows update to patch your compy with the appropriate security patches.
• install a good anti-virus prog
• install an up to date web browser
  
• use file setting, transfer to reinstall your
• Use sytem restore to make a backup of your nice fresh faced, lean & mean installation of XP (as mentioned previuosly)