I have a WD WD5000AAJS-00YFA0 that I purchased 2.5 years ago because my previous data storage drive was starting to fail. I managed to get most of the data back on this drive. Now, with no warning, this drive logically disappeared from my computer. Via BIOS, the machine knows something is there, but cannot pull any information (head/cylinders/model/etc). Other empty ports show "no drive". The port this drive is connected to just has no text. I took it to a spare PC I use for testing, same results. I have several small drives that I plugged into the same SATA port and they work just fine.

I'm used to drives failing by click of death, bad sectors, failing to copy files....but this is new to me.

I'm not afraid of getting a donor drive and swapping the boards, but I also heard you need to get the same firmware and such...if that is even the solution I need to go for. I'll definitely be doing a raid 1 for a little more protection.

I appreciate any help with this. thanks.

Probably the HDD has suffered no mechanical failure, but instead some operational dependent service modules have become damaged or corrupt somehow. Symptoms for this would be an apparently healthy drive with good initialization and no odd sounds, but just no ID. This is consistent with your BIOS identifying a presence but with no specific details on it.

You can use MHDD to check that it does reach DRDY + DSC status, but ideally your going to need to get this professionally diagnosed by someone with the right tools and experience.

I've run MHDD and it appears that it does reach DRDY/DRSC status, but that is as far as it goes. When selecting the drive, it states the drive does not support LBA mode and errors out stating the drive is not responding or operation cancelled.

I think I found a company that can replace the PCB relatively inexpensively, thanks to the help of his board. thanks.

WD5000 and similar do fail in this manner, and I am sorry to inform you that the reason can also be internal and require cleanroom work. Get the drive professionally diagnosed by someone who have the right and legit tools and if required can perform in-house cleanroom work if necessary, without having to send elsewhere an already opened drive.
50-60% of times I have seen this behaviour had to open the drive , having the rest already ruled out.