cannot get sims 2 expansion packs to install.

I put on my sims 2 and it installed fine. and ive got 3 expansion packs

university, family fun stuff and finally pets.

I know the order i install them in, and it goes uni, family, and then pets because it runs off pets. So it gets to the last stage of the installation of the sims 2 university, where it needs disc 4 to update. And i know ive installed the sims 2. and it tells me it cant update, or it cant copy the disc

Help please?

Consider that a blessing in disguise.......

Seriously though, the only thing I can think of is check all the discs and make sure they aren't dirty or scratched.