Unable to Submit form 

If the Submit button at the bottom of the form is grey rather than green (depending on your theme) then there may be a mandatory field in the form that has not been completed.   Once you complete/populate all the mandatory fields in forms, shown with a small red dot, then the submit button will change to green.  Note if the drop down is left as 'None' for a mandatory field then the Submit button will not be available to select 

It is good practice to click the save button before submitting forms.  Previous versions of contact/asset/case forms are available to see within the form page though. 

You can check if a field is mandatory by pressing tab through the fields. Mandatory fields will show warning error below.

Forms in Sharepoint 

Forms must be manually saved into sharepoint if required, they will not migrate over