It's too bad the support "engineer" you spoke to didn't know how to recover your situation. I understand what he tried to do, but there is another way he could have described to you enabling remote desktop connections and remote assistance that doesn't require the ActiveX plugin his system required.
In any case, it sounds like your system was very sick by then, so maybe or maybe not it would have made a diff.
It's likely when you were typing strange characters that you had some keyboard alternative key pressed. The idea of these special keys is that when pressed, it activates a "second set" of letters, numbers or symbols on the keyboard instead of what you'd normally expect. To undo that situation, you have to know what special alternative keyboard key you pressed, usually pressing that key again will return you to the normal keyboard
That's hard to fix remotely because every manufacturer's keyboard might have a different special key to do this... On my personal laptop I have not only the standard CTL and ALT keys, I also have the generally seen Windows key, a Fn key and another key I have no idea what it does (I hope I never have to find out or maybe I should find out now before it causes a problem?!)
The task manager is a special app which will list all programs running, all lower level processes running on your machine, some information about general performance plus more.
The Task Manager app can be invoked at least a couple ways...
While logged in with an Admin account, you can press CTL-ALT-DEL keys all at once, and one of the buttons you'll see on the window that pops up will be the Task Manager.
Another way is
Start Button > Run...
Type in
taskmgr
Good Luck...