Problem with US international keyboard layout: dead keys produce double characters

[Dajm]

I'm using the US International keyboard layout, which allows me to have access to French and German special characters.

It worked fine until 2 days ago. I have no idea what triggered this, but now, whenever I push the key for single quote, I get 2 single quotes on the screen.
If I push the key for a double-quote, I get 2 as well.
Same thing for the tilde-key and same thing for "shift 6": I get 2.

This means I'm currently not able to write any of the French letters with accents nor any of the German Umlaute.

From what I see, all keys that are supposed to be dead keys in this layout are acting up. Instead of waiting for my next input, it gives me 2 of whatever I pushed.

I have no clue what could have triggered this.

I think it can't be my keyboard's fault, since, if I switch to "English (US)" (the normal one, not the international one), everything is normal and quotes and double-quotes work fine.

This is on Windows XP, in case that matters.

I have another computer here with XP as well and the US international layout works fine without problems on it.

Any ideas? Am I missing something?

Is there maybe some weird Ctrl-Alt-something combo I might have accidentally pushed that could have caused my problem?

Thanks!

[Dajm]

Nobody with an idea of what it could be?

It''s driving me crazy! Aah! See? Two single quotes!

[Dajm]

Solved it. As incredible as it sounds (at least it did to me), the cause was a virus.
While I was working, all programs I had open (Outlook, Firefox, Skype, etc) suddenly shut down and a window appeared telling me I had a virus and I should run a scan and buy this software, blablabla. Your typical scam.
Long story short: Malwarebytes took care of the issue and everything's back to normal.