There are only two Tuning Adapters in existence, one made by Motorola, the other by Cisco. You mention Time Warner, so I suspect you have the Cisco version. You should see STA 1520 on the front of the device.
What's your geographical location? It's a bit surprising to hear you only have two tuners from the Tuning Adapter, that is a very old firmware version and should have been updated by Time Warner a few years ago.
Post back on the above items and we'll go from there. You might also try unplugging the Tuning Adapter for a minute, and then plug it back into to reboot it.