Yes. If you keep it well fed, and clean, and entertained. Your Sim will be in a good mood
Also you can look at its wish panel and see what it needs often. Make sure they have lots of sleep and treat your Sim to a day at the spa it will be happy. And if you promise a wish make sure you fulfil it because if you don't they will be miserable.
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Sims 2 is better, the graphics are better and there are more options.
buy a hot tub and sit in it for a while and you're sim will get to a better mood
maxmotives is the cheat that instantly puts your Sims in good moods and turns all mood bars green.
Well there is no cheat all you have to do is make your Sims do their homework. If you have Sims 2 Seasons you have your sim drink apple juice before they do their homework. It will help them do it faster.
Try Un installing some The Sims 2 Games if you have any, or Get some RAM