I lost my registration code

Try the steps in this link http://answers.ea.com/t5/The-Sims-3/FAQ-Lost-and-broken-DVDs-and-missing-serial-codes-What-to-do/td-p/14230

Lost/broken DVD but still have the serial code!

With your serial code, you are eligible for the download version of your game. You can download it through Origin and redeem your code.

Instructions on how to do this can be found here: Redeem Your Serial Code in Origin

Make sure to uninstall the DVD version and install the download version instead.

Finding your Registration / Serial Code

If you still have the game on your computer you can follow these steps to find your serial code from your registry (PC only). Credits of to Carl's Sims 3 Guide

You need to be signed in as an Administrator first.  Windows may require your permission to open the
Registry Editor and if so, just click on yes.

1. Press the Windows key on your keyboard and type regedit in the search bar and press Enter. 
2. Click on 'File' at the top left of the window that opens then click on Export.
3. Choose a location and name for the file as this will be your backup registry file.
4. Click Save.
5. This backup is created just as a precaution.

Now to find your serial codes for each specific EP or SP installed on your computer:

1. Expand the HKEY_LOCAL_MACHINE folder.
2. Expand the SOFTWARE folder (Wow6432Node for 64 bit systems)
3. Expand the Electronic Arts folder.
4. Expand the Sims folder
5. Expand the EP or SP you need the code for
6. Click on ergc and in the box to the right under 'Data' you will see the code
7. Write it down somewhere save
8. Repeat above steps for each EP

Once you have the serial codes written down just close the file.  If it asks you to save any changes, answer no.   If it did ask for changes then you didn't follow these steps.  I usually close the file by clicking on the red 'X' at the top right corner.
Please note:  NO CHANGES are made to the Registry if you follow these instructions so you have nothing to fear

Note: The above only applies to Windows PC's, if you have a Mac the codes should be here:
Users > Username > Library > Preferences > The Sims Preferences

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Instructions for Macs can be found here: Finding your serial key using Terminal

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Finding the code on Origin

If you registered the game on thesims3.com OR bought it on Origin, the serial code can be found in the myGames tab on the Origin client. Download the client from here http://origin.com/download, log in with your data and go to the MyGames tab. Move the cusor over the game and find the i. 

The product code listed there is your serial number (it can be different from your original one if the game was bought before Origin came out)

No access to the serial code

If you lost your serial code and don't have the game installed on an old computer, you need to contact Customer Support.

They can be found here: https://help.ea.com/contact-us

1. Click the link https://help.ea.com/en/contact-us/ask and log in with your Origin name and password.

2. Where it says: ’What Can We Help you With’, type in ‘GAME NAME’

3. Click Find Solutions

4. Select "Your problem,eg accounts" from the drop-down list and also select your platform from the list.

5. Click: Find Solutions

6. Scroll down a little and on the lower right hand side, Click "I Still need Help"

Picture to help you understand better,  https://help.ea.com/article/welcome-to-the-new-and-improved-ea-help-center

The Window Will Open...
You’ll now see the currently available contact options. These may vary depending on your geographical location and the time of day. Phone or Live Chat are the best options.

For customers in North America:

• Select "Call me."
• Enter your phone number.
• Select "Submit."

For Customers outside of North America:

• Go to the "choose a contact method" section
• Contact us using the telephone number provided within the listed opening hours

Please be aware that it is likely that the agent you speak to will need to confirm information on this account.

Hope this helps
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***Please note...I do not work for EA/Origin. Questions belong in the forums,Solution is like medicine,same medicine/solution may not work on same problem

I don't answer questions via PM.  AHQ is "Player-to-Player" technical self-help forum