Hi guys. I have a Barracuda ST1000M003 FW:HP13. Spins up, but is not detected, what should I check first???

Is not detected in BIOS or Windows ?
Check and clean power and SATA contacts. Carefully remove PCB (static sensitive both PCB and head !) and clean corresponding contacts.

Is not detected in Bios. I cleaned all the contacts, still not detected. I could flash the ROM, but I'm not sure what firmware should I look for? I heard the firmware is absolutely unique for every HDD. Is that true? Then, you cannot flash the ROM from an existing bin file? What should I do next? Thank for your help, Mia.

Try connect HDD to SATA and power supply on desktop computer.
Not the firmware is absolutely unique for every HDD. Unique contents of flash memory on controller PCB depend of heads and disks for every HDD. Get to Seagate site i.e. https://www.seagate.com/gb/en/support/k ... -223651en/
and find test and utility programm to check HDD and maybe flashing new firmware.