Big problem with Sims 3?

Hi, a lot time now I have a big problem with the Sims 3. I have all the expansions except Generations and Outdoor Living. So, about every 1 minute the game crashes for about 15-20 seconds. This has happened a lot of times before but it was fine after some adjustments. I have the game installed in an external hard-drive but it didn't bothered me before, I have lowered the graphics, I don't have the game in full size, and they are all originals. I believe it is because of my CPU but I don't really think so. What is your opinion and what should I do?