Lads, I know a bit about computers, and here are the few things I can think of that could be wrong:
Your computer can't see the disc:
There's a problem with your disc or your disc drive. Try another disc in your disc drive, see if it can see that. If that's OK, it's the disc, get a new one, or a disc doctor. If not, your drive's dead, no one on this forum seems to be too technically minded, so I'd suggest bringing your computer to a repair shop. If you are confident enough that you could repair it, google your problem, but don't do anything too drastic without the advice or supervision of a fully fledged computer geek :p
You've got a glitchy game:
There's a problem with your computer. Sims 3 needs a dual core processor, I've a 3.0 processor on my PC(XP) that is not dual core, and I get tonnes of glitchyness. I have a 2.6 dual core on my mac book(OSX), and it runs perfectly. Most XP computers never needed a dual core processor, (Vista is such an overloaded piece of c**p that you can't run it without one) so..
[I no what your problem is, my mums friend is friends with the people who make the disks, i asked her what was wrong (because it happend with mine) and i didnt have windows vista i had windows xp, and it only works on windows vista..] - popz
Is incorrect, it would work fine on an XP computer, if you had a dual core processor.
And just make sure you have at least 2 gigs of RAM and a decent vid card, mine's an nvidia, can't remeber the name but it's 256mb and seems to be working fine - But that's just for an enjoyable gaming experience with limited lag :)
Oh, and green discs are fine, I have one. I think they could just be the European edition.
Hope that helped,
Good luck everyone!