Sims 2 Pets Problem :(

I have vista for my computer and installing Sims 2 was fine.
I recently bought Sims 2 Pets and I installed it, all fine, until the update stage where I have to put disc 4 in.
I put the disc in and up comes this,' TS2UPDO.exe has stopped working' and BOOM! Installation terminated

So I download a Sims 2 Update Patch from the EA website and when I try and run it with disc 4 it says,' thesims2_update.exe has stopped working'
hmmm.

Just also, to point out, I can't actually open sims 2 from the desktop icon, I have to let the disc load and then run it and then allow the computer to access it.

WHAT THE HECK IS GOING ON!!
I really wanna play on petssss.