When Jeff Phelps started Bytes for a Bit in 1993, he envisioned a career of repairing the Commodore Amiga, which he thought would become the computer of the future. Way wrong was he, but thirteen years later Phelps remains fascinated by computers, and he does a brisk business solving software and hardware problems for businesses and consumers throughout the metropolitan area. Like a doctor from a bygone era, Phelps only makes housecalls. The first half-hour rings up at $65. Each additional hour costs $60. (The rate increases outside Bytes' coverage area: St. Louis and the counties of St. Louis, St. Charles and Jefferson.) Phelps says one of the most common problems he encounters is the dreaded hard-disk crash coupled with the user's failure to back up data. Get the hint? Here's another: Don't take matters into your own hands. "Some people try to do their own repairs, like by prying things off with screwdrivers, and they really botch things up. I had a doctor one time who got so frustrated he literally banged his computer with a hammer." Not good? "No!"