Ask any person who has worked in first line technical support and they will tell you that one of the most popular questions they get is that the @ key has changed position on the keyboard.
Nearly all of the time, the answer is down to the keyboard input layout being incorrectly setup, or for some reason has changed. Keyboard layouts vary depending on what country you live. Most people who notice that the @ key has been incorrectly placed will be from the United Kingdom and have set up their keyboard as the USA layout, or vice versa.
If this is indeed the case, a number of keys will actually be incorrectly placed, it just so happens that most people notice the @ key first, since this is one of the more popular keystrokes we’ll make on a keyboard.
Changing it isn’t difficult. Assuming you are using Windows 8 or 10, the answer lies within the Control Panel. Just go to the start menu/screen and type in “Control Panel” and make sure it is in Classic (small icon) view and select Language. On the right of your keyboard pack icon you will see a link called Options. Click that and under Input method select Add an Input Method. Then just select the relevant option.
For UK users, that is English United Kingdom. For US users, just US.
Once that is added you’ll see an option to remove the input layout you don’t want. Click Save and that should do the trick.