My suggestion would be to check on any trojan, virus and/or maleware. It is also possible that you got a Real Player update which messed up your player config. But that's just guessing from me.
To check your system I reckon several programs which are free and/or trial versions, which can be used even after the trial limit has passed (inclusive regular updates, which will still be possible):
Spybot - Search & Destroy (FREE) http://www.lavasoftusa.com/software/adaware/(free) http://www.grisoft.com (free and reliable AVG program) http://www.ewido.net (trial, which can be used after the end of the trial with regular updates) 