Double quote marks and @ symbol swapped!

I started using Scrivener a few days ago and everything was working fine. This afternoon, however, I’ve discovered a few of the keys on my keyboard have inexplicably swapped! When I press Ctrl+’ to get double quote marks (as per my keyboard) it displays a @ symbol instead. When I press Ctrl+@ it displays the double quote marks " ! There are a few other random character keys that are mixed up as well, all when the Ctrl key is pressed.
Can anyone enlighten me as to why this has suddenly started happening? I’ve had no problems before this afternoon and it hasn’t affected any other program (Word, IE, etc.). I’ve trawled through Options and cannot find anything that would have caused it. I’m using the Windows version of Scrivener.
Thanks in advance.

Sorry, where I referenced the Ctrl key I meant the Shift key! Shift+’ creates an @ symbol and Shift+@ creates a " . Seems to only be on that external keyboard I was using - the laptop keyboard is fine. Anyone know anything about keyboards?!