Haven't been able to play The Sims 3 since i built my new pc in december

neoromanempire​  Test the game and make sure it still doesn't work properly now.  If it doesn't, use the non-invasive way to change the location of Documents, restart your computer, view the registry again (like this) to make sure the change took hold, and try again to play.  The point is not so much how you change the location as the fact that viewing the registry is probably the most reliable way to check your work.