Media Player suddenly stopped working

Hi, I listen to internet radio and watch internet tv (streamed) through Media Player. A few weeks ago I could suddenly not listen to radio anymore, fortunately the site lets me choose between different players so I can still listen through Quicktime. Yesterday afternoon I watched a television show without problems but when I tried it yesterday evening all of a sudden it didn't work anymore. Unfortunately this site (nor all the other ones) does not give me the option to choose another player. I tried it again this morning but it still didn't work. I've tried it on another pc and it worked just fine.

What has happened to my pc and how can I solve it...?

Any comment is appreciated!

Have you tried System Restore and restoring the PC back to a date when it did work? If not, give that a try first. System Restore can be accessed from Start/Programs/Accessories/System Tools.