Hi Kimblog,
It has to do with plugins. There is no specific limit for plugins / widgets but from what you are saying, definitely you have some plugin which you have been using (and still not removed) which is conflicting with something else. To find out which one it is, I would recommend you the following:
1. Disable all current plugins.
2. Install a plugin which used to “crash” your admin portal.
3. Start enabling the old plugins one by one.
4. As soon as you get a blank screen or an error, it means that is the plugin which is conflicting. If you found it, try to find a replacement for it or contact the developer, maybe he or she knows of any existing conflicts.
To confirm that the plugin is causing problems, you might want to try again the whole process specified above with another plugin which earlier on gave you problems.