Need Help! Mac LC II won't boot from HD!

There is a forum specialized in 68k vintage Macs, I would recommend posting this there as well as you may get a quicker response:

https://68kmla.org/forums/

It's always a good idea to replace a weak/dead PRAM battery. The LC II uses a 3.6-volt, ½AA lithium battery. You can find them online for about $5, but you might also find them in any local battery-specialty retailers in your area. Certain alarm system components use that same battery. Whatever you do, don't go to one of the few remaining Radio Shack stores to buy one. They charge 3 - 4 times the going price online. As for the hard drive, although you hear the platter spinning, there could still be an electronic problem on its small circuit board that's causing it to not be recognized by HD SC Setup. Have you checked the motherboard for any evidence of damage to its electronic components, like leaking capacitors? The hard drive is a 50-pin SCSI I/II — either a Quantum 40, 80, or 160 GB drive, if it's the original. They are getting harder to find than they were, even 5-10 years ago. You can always check ebay for one, but be sure that the seller guarantees it to be working, because a used one of the same capacity will be just as old as the one that you have and likely have high mileage.

I agree with you. The only thing I have to add on with is that if your computer still has the original PRAM battery installed, REMOVE IT! Those things can explode, leaking acid all over the logic board - typically ruining the computer in the process.