During the installation of the game use one of the serial numbers listed here:
When starting the game, it asks for the first disc.
You do not have the original discs, so you do not have this one either.
To play the game, you have to:
- stop the game first
- copy the original program file sims2.exe (which usually resides in
"C:\Program Files\EA Games\Sims 2\TSBin\" or whatever comes close)
with the one enclosed here.
- Start the game