As the title says i have a Toshiba MK2565GSX - 250gb 2.5'' which is spinning, but it's not detected. BIOS doesn't detect it (tried it in two different laptops). I also tried with external power supply and sata to usb adapter - still not detected. I suspect that there is something wrong with the pcb, but i'm no expert.
There's important data on it and i want to recover it. Where should i start and how?

Spinning indicates that the PCB is likely fine.
More than likely problem is internal and possible firmware.
Any abnormal behavior by the drive prior to failure? E.g. slow, unresponsive at times, can't browse through folders, strange sounds?

Is the drive out of a laptop that may have been dropped?

What about strange sounds now?

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Hard Disk Drive (HDD), Solid State Drive (SSD, SATA, NVMe, etc), USB Flash Drive and RAID Data Recovery Specialist in Massachusetts

As far as i know the drive was in the laptop working fine. It haven't been dropped or anything.
The owner told me that everything was working fine when it suddenly started to work slow / lag and she restarted the laptop. Since that restart it stopped working (bios doesn't detect it). I haven't heard any abnormal sounds yet.

edit: If it's firmware - can i do something myself about it? ( i have experience in flashing usb flash drive's controller )

Flashing anything is not needed.

In terms of firmware, if needed at all, it may be a growing fault as result of the drive's deteriorated condition.
To address that issue, again if needed only, then advanced firmware tools are mandatory.

To maximize chances of recovery, a solid diagnostic is necessary in order to rule any mechanical issues.

For solid diagnostic, seek pro help that have advanced tools to test properly.
For DIY yourself diagnostic, hence not so solid, given that you realize causing more/permanent damage is of high possibility, you can run some brief tests with MHDD. See if the drive IDs correctly first and so on.

I suggest you practice on a identical/similar drive to see how it works, get a better understanding, and then move onto the failed drive.

Best wishes

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Hard Disk Drive (HDD), Solid State Drive (SSD, SATA, NVMe, etc), USB Flash Drive and RAID Data Recovery Specialist in Massachusetts

Since we don't have any decent experts at this area here in my town and my client won't give that much money for recovery i risked damaging it and tried mhdd as suggested, but mhdd doesn't detect it as well. When i power on the laptop and press the button for boot options menu it takes some time to pop up and when it does the hdd isn't one of the options. When i power off the laptop the hard drive makes a sound similar to clicking sound, but only when i power it off.

You may have more success connecting the drive to a tower machine directly to a SATA port.

One can't really hear well the drive's behavior unless placing the ear really close, like right against it.

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Hard Disk Drive (HDD), Solid State Drive (SSD, SATA, NVMe, etc), USB Flash Drive and RAID Data Recovery Specialist in Massachusetts

I expect to hear very quiet "brrr brrr brrr" retrying noises

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This problem maybe caused by FW problems or HSA problems i both cases you need experience an pro tools