First off, this is the wrong forum. You want the hardware and software issues forum.
Since it "always worked before", either something about your system has changed and it no longer supports Oblvion or your "not much scratched" cd has gone belly up, sorry. If you bought the game new perhaps Bethesda would replace the CD for a shipping charge. Try contacting their tech support. Or you could download the game from Steam for a lot less than 40 euros.
I'm assuming you have not installed any mods? Can you play other games on your system? A graphics card that's going bad can certainly cause crashes as can other system problems. But really, the best possible news for you is that your cd is bad. It's gonna be much cheaper to replace than anything else.
Edit: Do you have access to any other system that would run Oblvion? Like a friend or relative's system? You could try a test install on that to see if it is indeed your cd.
Mara