I previously tried resetting Mica’s BIOS by both using the reset jumper and pulling the CMOS battery for a long time (hours). This morning I successfully reset it using the jumper method, but the difference is that I used another (unused) mainboard’s jumper instead of scavenging the one used for JPCOM1 on from Mica’s mainboard:
All settings have reset to default now - my best guess is that it wouldn’t boot before without the COM jumper making some sort of selection? Not sure.