...they erase practically everything each time they work on it.
A "clean" installation sounds like a good thing.
However, since the last repair I am unable to type a forward slash or a question mark (which appear on the same keyboard key).
What do you think of that....
cccmedia in Quito
Then yes, that sounds like what they did. As you've probably gathered by the name, the clean installation is simply where they take an installation disk and re-install WIndows to your hard drive,overwriting/deleting what was already there. In doing so, it's a fresh start, no errors, viruses, etc., but also no drivers or updates, You also lose any programs and personalizations which have been added. Sometimes a clean installation is a necessary step, but other times it's just a quick shortcut to fix a problem, but at the expense of all those programs and personalizations being lost. If they have done that every time you've brought the computer in to them, it sounds like they're a little "clean installation" happy.
So far as your keyboard, from the Windows button in lower left-hand corner, do a search for "Change keyboards or other input methods". Or you can search for that within Control Panel under "Clock, Language, and Region". Make sure your keyboard United States English, assuming that's your preference. The disk image they may have used to re-install Windows may have been from another similar computer, though one which had its settings to a different language's keyboard. That particular key may just have happened to go out, but I really doubt that. Too coincidental.
You'll also want drivers to be updated for your computer. Also something that they should do when performing a clean installation, but perhaps they didn't. Many drivers are now built into the regular WIndows updates, so if you just search for "Windows Update", it will take you to the option to "Check for Updates". Just be ready, though. If they did a clean installation and didn't update for you, then you're going to have at least one hefty update file (>500 mb) to download, with multiple smaller ones to follow. Hopefully you have good broadband. If not, perhaps bring it back to them and ask that they apply the updates with their bandwidth.