if the pads are original and haven't been changed, there's a good chance they'll need replacing
They probably needed replacing 10-20 years ago!
Before replacement pads became available, we all were making our own, so that's an option if you need only a couple, or suppliers have no stock, but beware that it is not a quick project to make all those pads by hand ...
https://lisafaq.sunder.net/lisafaq-hw-kb_repair.htmlThe density of the foam affects the feel of the keys when they bottom out, but doesn't seem to matter otherwise. I think closed cell foam may last longer.
Note that the metallic disk doesn't actually make electrical contact with the circuit board, so eg. you can't just replace with aluminum tape. Best to reuse the two disks from each key and replace the foam between them.
the keyboard is not responding at all
Although the pads certainly need replacing, there also could be an issue with the wiring in the chassis that connects the keyboard plug to the motherboard, or even a dead keyboard. Once you get the keyboard apart, you could test the bare circuit board by putting one of the insulated disks onto one of the key locations to see if that is recognized by the Lisa.
