could be a whole number of things, do you have a USB mouse and does that work okay?. Is your system fully up-to-date?.
Have you considered an upgrade to UM 20.04 as the support for 19.04 has reached its end?.
If you have a root and home partition setup, you could take the easy route by using the "Something Else Method". If you update via the normal way, you will first have to update to 19.10 and then 20.04!.