UR22 not recognizing sound input

I just bought a used UR22, and the 6,3mm jack inputs are like dead. They recognize no audio input, even if I have the volume at full on everything. I’ve tried two audio cables, two USB cables, nothing. I tried my microphone with XLR, and when I yelled into it with my hand wrapped around it, I got some clippy recording with Audacity. As for instruments, I tried my electric guitar and analog synth. But it won’t even peak.

Also +48V phantom power just makes the USB and PEAK lights go crazy.

EDIT: I got the thing in this weird state. Now the input pulses, depending on the frequency of the sound that’s coming in. And only with low frequencies. I mean, like (example) play a C3, sound comes in and out in a pulse, wow-wow-wow. C2, that pulse becomes slower. Too high note, and suggenly no audio again.