As Gamewarden alluded to, we would need to see the settings you have under the alignment tab. First, check the box "Highlight Detected Stars" so you can see what, if anything, is being detected as stars. Begin by increasing the digital gain setting, one step at a time. If there are obvious large bright stars that are not being detected, try increasing the Maximum star width. If there are tiny stars that you can see, but that are not being detected, you can try lowering the Minimum star width. You can also try lowering the Black level threshold and the reduce noise setting.
If it then starts detecting plenty of stars, make sure they are actually stars and not hot pixels or noise (or simply too many stars). If so, then increase the noise reduction and/or the black level threshold.
Alas, if your FOV is very small, there may well be times that not enough stars will be visible to SharpCap to align the frames.
Hope this helps.