|Stop any programs that startup with Windows (except anti-virus/anti-malware or firewall). Having too many things running in the background is usually the culprit.|
Have you done a full virus/malware scan of the machine? Virii/malware can use a lot of valuable resources. Scan regularly with an updated set of definitions.
Delete unneeded files and uninstall unused programs. Clutter will cause performance problems (the worse the clutter, the worse the problems). CCleaner (freeware) is useful for regular clearing of trash files and accumulated log files etc.
Use a trusted registry cleaner to clear unwanted/ unneeded entries. CCleaner has one built-in that has never given me any cause to distrust it.
Adding more RAM can provide a performance boost. It's the cheapest upgrade you can give your machine.
How long since you defragged? To be honest, I don't find a lot of benefit in defragging often, but some people say it's a must.
If all else fails, do a clean install of Windows. Sometimes starting over is the simplest option. If that fails to improve performance, it's time for a new machine.
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