I think you need to add more memory.
Also clean your registry to run computer at optimal state.
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Speed Up your computer now.

Running slowly could be a lot of things. It could be you don't have enough physical memory (RAM) in your computer to do what you want. Less than 1 or 2 GB might be seen as slow. If you really want to reinstall Windows, back up all the files you want to save to someplace else, like an external hard drive or thumb drive. You will have to reinstall all your programs (Office, etc) after you reinstall Windows. Take the CD copy of Windows that came with your computer and boot your computer to that. You may have to change the boot order by entering Setup (usually by pressing F2 when it starts). Make sure the CD drive is first in Boot Order. When you boot to the CD follow the instructions for installing Windows in the screens which follow. Delete any existing partitions and install it on a clean partition.
Good luck!