there are soo many possibilities, unfortunately with what you posted we can only guess as to what the problem is. can you please post the crash log?
When did this issue start? did this happened immediately after an update? you new here? I know after this last update MANY people have had issues of all sorts, there is no 1 problem causing it.
To some of you that posted, you are starting a new mods folder after the update right? adding in an old one that was prior to the update will not work you need to start over and add back in , there are newer files every update and can throw everything out of whack