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help! my computer is making extra clicks and keystrokes. what to do?

For example, when I click once, sometimes it clicks twice. or clicks three times when i double-click. Also, when I'm typing, sometimes letters are doubled. Oh, and when I'm dragging files and folders, it doesn't drag continually but "drops" them randomly, as if I'm letting go of the mouse button.
I have windows 7.
Please help, if you don't know how, at least give an idea or something. Or, if you don't know how to fix it, let me know at least what the problem might be.
I know it's probably not hardware, or else it wouldn't affect the mouse and the keyboard. I know I could just reinstall my OS, but I'd really rather not right now XD
thanks

I recommend either:
1. checking the sensitivity and other settings of hardware in the control panel
2. do a quick virus scan to see if it is a virus that is affecting it (many people think viruses have a very large impact on how your computer functions, but it can do something as simple as change the sensitivity of a click.)