Do 2.5" SATA HDDs in an external enclosure need extra power over USB with Windows? MacBook Pro 2008 motherboard failed. Upon sending it to an Apple authorized repair center, they confirmed this. They gave me the laptop back so I could open 'er up and get the hard disk out, which I did. The hard disk should be undamaged.

However, upon plugging it into an external enclosure – and connecting the enclosure to a computer running Windows – there's power, but nothing seems to happen. I'm just powering over USB. I wouldn't expect the HDD to be dead as well as the motherboard.

Does the 2.5" SATA HDD from a 2008 MacBook Pro need extra power when connected in that way?
What is the exact make and model of external enclosure you are using? Some of them require an external AC adaptor. Some of them come with a duplex (two-headed) USB cable and require that both of them be plugged in to powered USB sources to provide enough voltage to run the enclosure and the drive.

Of course it is possible that your hard drive itself is damaged. If that is the case, you will need to pay a lot of money to a specialty hard disk data recovery service.

Finally, do you not already have a Time Machine backup of your Mac's internal hard drive to an external disk drive? When this current situation is resolved, it would be wise to invest in an external backup system using Time Machine.

UPDATE:

Have you tried this drive in a different external enclosure? until you do that, you can't rule out that it's the external enclosure's problem and not the drive's problem.