Ok, not that I'm an expert in this field, but I do have a business that does PC Repairs.
There are a couple utilities that you must have to keep your computer running. They're all freeware, and are must downloads.
1st. Remove your antivirus client. Get rid of it.
2nd. Download the following Security Apps and update them, and then do a scan:
Malwarebytes
http://www.download.com/Malwarebytes-Anti-....html?tag=mncol
3rd Download the following maintenance programs
Advanced System Care
http://www.download.com/Advanced-SystemCar....html?tag=mncol
ATF Cleaner (Safer than CCleaner)
http://www.download.com/ATF-Cleaner/3000-1....html?tag=mncol
Glary Utilities
http://www.download.com/Glary-Utilities/30....html?tag=mncol
Pagefile Defragment (Microsoft Powertoy)
http://technet.microsoft.com/en-us/sysinte...s/bb897426.aspx
(XP ONLY)
NT Registry Optimizer
http://www.larshederer.homepage.t-online.de/erunt/
Smart Defragment
http://www.download.com/Smart-Defrag/3000-....html?tag=mncol
Run each tool and make sure in the options you have turned off smart defrag's auto defrag and that when you close it it actually closes and doesn't minimize to the system tray. Also do the same for advanced system care.
By running these, and then following the following instructions for an xp machine here: You can make your XP slim and fast.
http://www.debate.com/forums/technology/topic/699/
Also if you wish, I have my personal registry hacks here: (FOR THE XP USER ONLY) They also include indepth explanations of each registry change.
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