Did you uninstall it at any point? That'd be the only reason I can think of it not being there...
No. It's still on my computer. I just don't have the disk to play it.
But, I have Sims 2 Double Deluxe, not just Sims 2, I'm not sure if this'll help, though.
Because they're basically the same, except TS2DD has an expansion pack and a stuff pack already in it.