Re: education ... "I guess here (europe) it can be a professional baccalaureate in technical college with option school of management if you really plan to open a repair shop."
I know Europe is different, but I took that to mean the US equivalent of a degree from a trade school (like Heald, DeVry, et al) with maybe a community college degree in Business or Management. You're not trying to work for Microsoft or get a corporate gig, so you don't really need to impress anyone with a MBA or bachelor's degree in Computer Science.
TBH, I doubt most customers know or care about the credentials of the guy in their repair shop, they only care that the guy seems to know what he's doing. So what you need is enough education or background experience that you actually do know what you're doing.
FWIW, I would suggest *not* opening a repair shop until you've built a reputation or following. The overhead will kill you before you can get yourself established. Michael Dell started in a dorm room, building computers for his fellow students before creating his own company.
I would likewise shy away from sales because maintaining inventory is fraught with problems. Take hard drives, for example. You'd have to maintain an inventory because if a customer can't walk in and pick it up, he'll just get it from Amazon. And if you do maintain an inventory, prices will have dropped before you can sell your inventory at the price you paid for it, so you'll have to sell at a loss.
My recommendation would be to "back into it". Volunteer at a local senior center or the like, helping with tutoring, virus cleanup, simple repairs and upgrades, etc. If you're any good, you'll build a reputation, and you'll gain valuable education in learning how to deal with "customers" to keep them coming back. You'll also gain a perspective of what kind of need there is for your talents in your area. Is it repairs? Upgrades? Basic tutoring? Email/web help? Tablets? Cell phones? Don't try to monetize every minute of your time right away, but you should be able to begin building a side business of for-pay gigs outside of the senior center.
Seniors are also invaluable to word-of-mouth advertising. Unlike millenials, who change allegiances like they change their underwear, seniors will be fiercely loyal if you do a good job for them, and spread your name to everyone they meet. I can't tell you how many of them ask for extra business cards so they can pass them out to their friends. Eventually you'll start getting calls from people you don't know for, "I'm getting popups, do you clean computers?" "My computer is slow, do you do upgrades?" "Can you make me a website?" "Can you upgrade my computer to Windows 10?" "My computer says I need to upgrade Quicken."
If you really want to open a storefront, you might be able to parlay those side gigs into a brick-and-mortar existence. But there's also a niche for free-lance computer techs who work out of the house and market themselves to small businesses. Small businesses aren't big enough to hire and maintain their own IT staffs, but still need regular IT help and can be a steadier source of income than relying solely on home users.
