turn off solo take gimbal and cover off, you see that button inside there where it says sswt hold it down and turn on solo while continuing to hold the button in, once it starts you will here the typical start up sound that will turn into a different tone this is the pixhawk resetting, it will go through led flashing lights and should reset with white/blue leds up front and red in rear, if it does not check the orange led near the pairing hole/button it should be slowly blinking, if not reset the solo using the factory reset procedure.
Once booted check the orange led again it should be blinking on off very slowly, if not the computer did not boot properly and it may be a dislodged SD card inside the solo, as that is where the boot code is stored...good luck
one other thing if you factory reset solo you will have to reset the controller also or they will not talk to one another period.