Derek Cupanic started Canoga Park-based Computer Doctor in 1985, when far fewer people were buying computers. Back then, the company sold hardware and software. But with the emergence of much larger competitors like Best Buy and Fry’s that offer very low prices, smaller computer retailers have had to change their line of business to survive. Now Computer Doctor mainly repairs computers and trains people on how to use them. Cupanic spoke to reporter Jennifer Netherby recently about his business. “I have been doing this for over 20 years now. We do data retrieval, we fix computers, replace parts. I started the business after being disabled in a construction accident. Two weeks after the Mac came out, I built my own computer. We started Computer Doctor originally to build and sell computers. Then we changed and handled upgrades, and then repairs. “Business has changed over the last 15 years from selling hardware and software to teaching people to use e-mail and the Internet. We’ve gone from heavy hardware sales to support. Our customers are everybody. We have businesses, home users, movie studios, celebrities a lot of celebrities. We don’t work on mainframe. We mainly help fix PCs. “Usually the problem is a virus or someone trying to do an upgrade or something that didn’t work. We’re like forensic doctors. We also do a lot of computer tune-ups. After being used for six months or more, a lot of stuff ends up on a computer that people don’t know how to get rid of, that makes the computer crash or wastes space. We clean it up and put things back where they should be. “Most repairs range between $100 and $300. More than that and it’s not economical. We recommend they upgrade to a new computer. “Who is our competition? Most of the big stores (Comp USA, Fry’s) are for new buyers. Our competitors are other small repair shops. We’re not like your regular computer repair shop. Most shops focus on replacing parts. We diagnose the problem and fix it. “We also do tutoring. It’s mostly for somebody who just bought a new computer and doesn’t have a clue how to use it. They usually just want to know how to use it safely.”