Good news folks! Problem solved thanks to Retibika. I've always used only one account on my computer, the administrator account. So I did as Mr. Retibika here suggested, and created a new profile. When I logged into the new account the MSN tingy worked just fine. But the wirdest thing is that when I then changed back to the old admin account it worked there too!! So I just deleted the new profile and everything's back to normal now. I have no clue whatsoever to WHY this problem occured in the first place or why making a new profile fixed it, but I couldn't care less right now cuz everything is working properly again
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Thanks a lot Retibika! You have no idea how much time and effort I have used on this shitty little problem.