Hi,
I've been playing the sims 3 for quite a while now and I never had any problem running te game. Since a week or two, the game is very slow! My computer can definately run the game, because I gave it (with the gamebox) to my computershop, so that they would increase the Ram or whatever I needed more for the game.

CPU: Intel(R) Pentium(R) 4 CPU 3.06GHz
CPU speed: 3.06 GHz
RAM: 2.0 GB
OS: Microsoft Windows XP Home Edition Service Pack 3 (build 2600)
Video Card:
Video RAM 512.0 MB
3D Yes
Pixel Shader version 3.0
Free disc space: 114.1 GB

You haven't given us your full specs (instructions on doing so are here: Game Help:System Specs^wiki), but I can tell you already that your CPU is not sufficient to play TS3, and your RAM just barely scrapes through. When you take your computer into a shop, tell them exactly what you want - don't leave it up to them.