But for so long?
What is the last update number?
Empty your community folder and put the addons in there one by one, restart the sim after every one of them and see when it goes wrong. Oh, and I think people here would appreciate learning when/with what addon things went wrong.
Have you looked at the administrative events in the event viewer of Windows? If the sim blocks, you should be able to see in the event viewer what went wrong with which addon.
Priller
Yep - bad repaints seem to be a common cause. It could be that it was a sloppy assembly to begin with, or it could also be that it was done prior to an update that rendered it unusable. That second option is more common than most would imagine.