Re: Burning smell from my computer.
Did you check the power supply? That would be my best bet as Retail companies put power supplies in their machines that are "good enough" sometimes they last, sometimes they do not. Also, check for Dust around your processor. My first computer once had a burning smell, but unlike you, I never cleaned it out. Turns out the burning smell was dust on the heatsink that got hot enough to make the dust have a strong burning smell. (that and the thermal paste wasn't so good).
Nine years is about how old my first computer was (still runs today). It really is time to replace something that old. After about 6 years (depending on how much you spent) computers become pretty much garbage without upgrades.
Sorry for the rambling, bottom line: check the power supply first to ensure it is functioning, then processor or any other critical system component for dust.