I visit my mom once a year, and usually perform preventative maintenance on her computer. Scrubbing it for viruses, applying updates for drivers, etc. On one such occasion in the early days, she complained that the PC was slow, and would quit. I opened it up, and there was a 1/4 inch layer of dust everywhere, and any and all vents were completely blocked, to the point that fans weren't turning. I blew that crap out, and from that point on became her IT guy.