Hi Lance,
3 years is quite a bit of time for any scope and your DPO7104C to have a solution for you without physically having your scope to diagnose.
We do have a service manual if you want to keep troubleshooting and replace parts:
https://www.tek.com/en/oscilloscope/dpo70000-mso70000-manual-6
Otherwise, you'll have to send it in for repair. This scope is under full support, though warranty for your scope ended 1 year after you initially purchased it.
https://www.tek.com/en/services/test-equipment-repair/rma-request
-Iris