when i worked at the hospital (yes this was a hospital that you'd expect to be clean) - we'd routinely find computers like this (well substitute dust for cat hair) i took a call once about a monitor not working. monitor worked fine but it was getting no input from the computer. Took it back to the office and opened it up. Immediately took it outside and with an intern's help first shook all the dust out (more like dust puppies the size of my fist then just just). then (while outside) i took an entire can of air to it as well. Finally took it back inside removed the video card and re-seated it (after giving it the can of air once more) and low and behold if the silly thing didn't work fine after that. at least it wasn't in a patent care area. I showed it to my boss and about a month later he sent crews of interns around "to maintenance" all the new computers (about a year old of which this example was one)