Everything is bold or italic, help

[Zeating]

A few days ago my fonts started to look italic for no reason, in my browser, email, Word, pretty much everywhere. The culprit seems to be Arial.
But when I open up the Arial font in the font viewer, it looks normal.
If I type in Arial in Word, it's italic automatically and CTRL+I makes no difference.
Google and Wikipedia always show up as italic now, and it's very annoying!!