Hey, my dad's old Gateway machine from '99 looked like that.
Well... not quite as bad. He gets a lot of hand-me-downs from me such as old hard drives, zip drives, video cards, network, modem, etc and that usually requires opening up the case and doing a little cleaning as well.
This is why I want a totally passive cooling system, no airflow issues and dust to worry about, kinda conflicts with my desire to get a high power gaming machine though, and I don't have the cash to get both.
