Hello Caroline,

I spent some time researching your problem. I read about several possible solutions to similar Sims 3 problems. I will narrow it down to 2 for your specific problem.

Please do the following first. Even if your Sims 3 is working 100% with no problems I still recommend doing this to make sure Sims 3 will properly update with any new fixes, patches, etc.
1. Restart your computer

2. Update your version of Windows using Windows Update. Update as many items as possible

3. Note: During the Windows Update it may ask you to restart your computer. Do so. After the restart open up Windows Update and finish installing the other updates. Repeat the process until there are no more updates to be downloaded and installed

4. Restart your PC

5. Attempt to launch Sims 3 using the play button again

ONLY IF THE ABOVE FAILS go on to the next fix...
1. Open up, "Computer" or "My Computer" (depending on what Windows you have)

2. Go into your "C" drive and go into the "C:\Program Files\Electronic Arts\The Sims 3\Game\Bin\" folder

3. Find the "TS3.exe" file and Double-Click it to run Sims 3

Please post what happens and what worked or didn't work :-)