Normally, a sudden crash of the client is a symptom of a bad client cache or versions of the components not being on the same build.
The client cache is normally under the folder path "%appdata%\..\Local\" (Windows 2008) and the file extension is AUC. Close the client and delete the files. They will be rebuilt by the client when it starts if needed.
The components you should make sure are aligned are Client, AOS-Service and Application (SYS+SYP).
The help dialog will reveal Client and Application, but not the AOS-Service (by default). You can head over to the Service binaries (dlls) where the service is installed, sort them by date and find one with the Microsoft.Dynamics namespace/nameconvention, right-click, Properties, Details and have a look at the version. It should be aligned with the version of the Client and application.
Another thing that might cause sudden crash is the UserData being incompatible with the actual current application metadata. You will find userdata within the AX Client, but removing ALL userdata will probably result in frustrated users. ;-)
Try to narrow down what exact element has invalid userdata, and remove the userdata for that exact element.
Good luck!