I was just going to say the same, USB power does not always supply enough juice for a phantom powered microphone.
If not possibly the mike, the cable or the interface is broken. Only way to test is to replace each item.
There is no mix control software for the Solo so all monitoring is done on the sparse front panel.
My son in Law has one and we had no problem setting him up with a SM 58, The pre amp level is at about 12 o clock.
Sing your loudest parts into the mike and turn the Level up until the ring turns Red then back it off until it stay's Green.
If you end up with the level control anywhere past 3 o clock, something is broken.