You could do it at a kiosk, probably, if you had a safe way to store laptops.

Drop ’em off one day, pick ’em up a day later. Certain problems resolved; others perhaps not, but much like a dry cleaner’s for your laptop’s software problems. Heck, if you had a storefront and two guys, maybe you could get same-day on a bunch of things.

Specialize in laptops, because they’re smaller and easier to deal with than desktops. (Also, because you don’t need to hook much up to make them work.) Do it at mall kiosks for all the people who walk by regularly; if you can, do it on a mall very near to a college campus. Even if the school does offer free computer support, I suspect that you could very quickly become more trusted than the school’s tech people, just so long as you were competent.