Recording MIDI

I'm not sure what to do now. I have the other tracks drums, bass, guitar in place. Trying to record Sonar SI-3 strings onto the track.
When armed for recording, I hear them, the levels are moving up and down like they are recording, but when I go back to listen, no SI-strings. This is the first time I've tried to incorporate Sonar digital music so I'm not sure what to do. I have checked the inputs and outputs of devices and everything looks right. I'm running a Tascam US-1800 interface for everything and it's already been replaced by a newer version, so I can't update the drivers. Any advice?
Thanks

Hi. Are you using separate Audio and MIDI tracks, or do you use Simple Instrument Tracks (SIT) when trying to record MIDI? If you open Piano Roll View ((PRV), shortcut Alt+2, IIRC), do you see notes after recording? Do you use a MIDI controller of some sort? If so, is it available under Preferences (P), MIDI, Devices?
That is all I could think of for now.
All the best.

everything these guys said applies. ijust wanted to add that inserting a soft synth in the way described will give you that soft synth as an output option in your drop down list.