Are you ready to go? Everything backed up just in case?
Now the fun part begins. Remove your Downloads folder. Cut ... paste. Put it somewhere else on your desktop ... just not in the EA Games folder. Run the game. Don't worry ... unless there is something really messed-up with your game, it will run just fine without the folder.
Go into a few households and play for several minutes. I find it's not a good idea to play for just a minute or two. A few minutes is better. In the rare instance that a house or Sim is corrupted, removing the CC might just delay a crash ... not prevent it. At least that has been my experience.
Are your Sims doing just fine? Can you get into the houses, and do your pixel dollies move around with no problem? Then it is almost certain that you have a custom content problem. Get out of the game. Don't save anything.
The most well-known way to go about isolating the problem file is called the 50/50 method. Put the first half of your Downloads back into your game. You can simply make a new folder in the game, label it "Downloads", and copy and paste the first half from the "real" folder on your desktop. I do that.
Go back to your game, enter the houses again, watch your Sims. Still fine? Great! The bad file isn't in there. Take the second half and try the same thing.
If, however, your game is acting up again, the problem is in the first half of your folder. You will now have to remove half of that section temporarily (and I think this shows why backing up your Downloads is a very, very good idea ... it's very easy to delete files by accident!) Try it again. OK? Great. Those files are fine. Not OK. Don't go any further. The problem file is in that first section.
Keep taking sections, testing them, moving on. Never save the game at any point. If you are doing this correctly, you should be able to isolate the problem file or files eventually. Usually, the problem involves a hack or mod, but
not always. Don't presume it's a hack or mod right away. Twice, I found that a wall caused problems in my game. That is very rare, but things like that do happen.
A "bad" piece of content, by the way, may not necessarily be "bad" for others. Perhaps the content involved an EP you don't have. Perhaps the creator didn't realize that the content needed Free Time, for instance, or you didn't read the description correctly. (I've done that.
) Perhaps the game had a conflicting item that the creator wasn't aware would cause problems. Give the item a quick "Google", staying away from unfamiliar Sims 2 sites. (Mod: Is it OK to specify certain sites?) Often, others have had the same problem. If you don't find any info about this mod or hack, and want to be nice, you can PM or e-mail the creator and mention the problem, if the creator is available. Be polite. Please be polite. Give some of your specs (what EPs you have, your basic system requirements, etc.). I find that if you don't act like a jerk, most creators actually want to know if their item is causing problems.
However ...
If you are still having problems, then a few things could be possible. In certain cases, your characters or lot could be glitched. Sometimes, even with your best efforts, it happens. Others might have better advice than I here, but I find that the best thing to do is to move everyone out and see if they do OK on a new lot. If they do fine there, it's the house. Get rid of it if you've created it. If it's a Maxis house with graves or urns, I would probably just keep the house there and not play it anymore.
If it's a glitched Sim, you might want to try to find which one is glitched, if possible. If adults, move certain members out. If a teen, try to move him or her to a university, if you have that EP. Some glitches actually disappear once you age a Sim. Many don't, though. Then it's time to eliminate that Sim. Never, never, never put the Sim in the Sim Bin and delete it. That can cause problems in your game, and these problems might not surface for months ... even years, as in my case with my Pleasantview. Kill your Sim off. Cowplants work nicely, for instance.
If all houses or all Sims have this problem. though, it's not the house or Sim. You have other problems with which more qualified people here can assist you.
Personally, I found that most Sims glitches outside of hardware issues (video cards, for instance) involved content. About 5% of my issues involved a glitched Sim or lot.
Good luck!