Why does the computer not show the hard drive?

Question

Computers

Hello dear ladies and gentlemen!
Yesterday I cleaned my computer from black layers of dust, carefully. Disconnected the plugs, then plugged back in. Hard drive Western Digital 20EARS-00mvwb0 2TB. PC, Win7 x64, stopped seeing in BIOS and in "Management -> Computer Management", well, in general, on the computer as a whole. The plugs seem to be connected normally, but they work on the old HDD. There were always programs on the computer to check disks, heaps, there were no prerequisites for a breakdown at all. I thought that the plugs do not connect well, I took another WB 500 GB, the old one, connected it and earned it under these plugs. I removed this disk, tried to insert it into the plugs of an older computer, it doesn’t work there either (probably this is done or not, I don’t know). Another thought was to connect directly via USB, but I don’t have such a thing.
There is a portable HDD, WB, it is also connected via USB, a big black box, you can’t seem to open it in any way - I just wanted to change it and try to use it directly. I will be glad to all advice. I apologize for your wasted time.
I've never come across something like this, I'm not good at it
. Thank you!

Answer 1

I read the comments, everything seems to indicate a lack of power. And among the "power" faults there is one specific, it would also be worth checking. This is a defect in the SATA power plug - it sometimes swells a little, and the contacts in the middle do not reach the disk contacts.
As I understand it, you used this drive on a relatively old power supply that did not have SATA tails, and connected the power through a molex-sata adapter. When testing the disk on another computer, was it fed through the same adapter? If yes, then here is the answer - replace it.

Answer 2

If you connected the disk with different plugs to several computers and the disk did not come to life, it died.