Lots of reasons, probably you downloaded or played corrupted data. Hacking is so advanced these days that embedding crap into data flowing through a network is not that hard to do - however illegal.

On the other hand you could have installed or removed something that messed with system files, more likely. How about checking cache and temporary directories, how about checking the cookies folders?
Extensions is raa or something like it, can't recall.

Last RealAudio along with MS get real mean if you use their stuff and
do not pay for it, so for example you'll often see folks online with older versions of Winderz - not licensed - having real problems with mouse, hard disk drives etc. This is no accident! They send out data
over the net to interrogate PCs to see if they are legal, if not code
is then sent to break the PC. Again it is illegal but hey nearly impossible to prosecute.

In the years I have been using the internet two things seem to be universaly true, mRC and Realplayer are Hacker hangouts. Neither are on any MS machine I use, though I would not be bothered about them in a Unix system such as Linux - since hacking into another persons Unix system is like attacking the US Airforce with a feather, talk about
turning diodes into transistors - hot hot hot! It should be outlawed!

lol