Macintosh classic hard drive failure

I've had a 1991 Macintosh Classic since about 2020, which I occasionally like to use for writing, gaming, etc...

Today, while trying to restart it, it ran ran into a problem: I was stuck on a blank screen, with only the mouse's cursor I could move around.

Not having much experience of electronics, I opened it anyways, and after a few tests I realised that the problem was with the hard disk (original, supplied with the Macintosh when I bought it, 40MB) which froze the device whenever I tried plugging it in.

I've tried everything: leaving it plugged in while unplugging the floppy disk drive (FDD), plugging the FDD back in while running with the HDD plugged in, without plugging it back in and turning on the system from the ROM (Option+Apple+X+O), plugging it in at various stages of bootup, etc... Whatever I do, as soon as the disk's 4-pin power cable is plugged in, the whole computer freezes, and only a manual reboot (using the power button on the back of the machine) fixes it. I also tried using the ‘reset’ and ‘interrupt’ buttons on the side pannel, but nothing seemed to help. However, when it's plugged in, the drive seems to be spinning, I can hear it starting up and spinning :(

I've also cleaned everything with IPA and a qtip, checked the capacitors for leaks (none in sight), yet the problem persists.

Does anyone have any idea on what the problem could be? I'm a bit of a noob at "older" electronics/informatics, so I've mostly followed advice I saw on other forums/posts. I can also send pictures if these are needed.

P.S : it's running system 6.0.3, if it can be any useful.