Make sure of these things:
- The receiver is set to accept signals from a standard DirecTV remote. There are two other settings, UHF (for people who have the box out of line of sight with the remote) and Receiver 2 (for places like bars and such that have multiple receivers stacked together, so these can be controled independently). You check and change this in the menu screen under setup.
- The remote is set to send a Receiver 1 signal. It is possible to change the remote to Receiver 2 accidentally.
If both of those fail, you can generally pick up a standard DirecTV remote at a place like Best Buy, which is a getittoday option over ordering from customer service.