Was it working recently? If so it could be that the adapter blew. If you just pulled it out of storage, couldn’t find the adapter, and tried a random one, that’s probably the problem. Model 1 takes a 9V DC adapter with reverse polarity from most other things (positive outside, negative inside), and if you use the wrong polarity or voltage it’s not going to work (and you could break the console). Other than that I don’t what could be the problem, I have some power issues with mine as well, that’s what I came on here for lol.
The lens has strong magnets in it that will attract the screw unless you're using a magnetic screwdriver of the exact right size. I also had to tape the back of the lens to the table so it didn't move, as well as tape the bracket in the right place.
For the smaller two cables, push the brown plastic piece away from the white piece to release. For the bigger cable, the brown piece is on a small hinge and you need to rotate it towards the white piece to release.
You first have to detach the foam on the front in order to take the cover off because the foam is gluing the two halves together. Just slide a spudger underneath it along the bottom and sides, making sure you're actually going underneath it and not tearing it.