Your Main needs to print the value returned by findmin, currently it call findmin but does not do anything with the returned value.
You have;
printf("the elements in linked list are: ");
display(start);
printf("The minimum element in the linked list is");
findmin(start);
Try;
printf("the elements in linked list are: ");
display(start);
printf("The minimum element in the linked list is %d", findmin(start));