These LC475 computers have issues with needing capacitors redone on both the motherboard AND the power supply.
That is very symptomatic of a motherboard recap being required. Also, did you change the PRAM battery? These require a good PRAM battery to turn on.
You can 'jumpstart' one of these with failing capacitors by turning it on, letting it sit for a few seconds, and very quickly switching it off and on (so fast it doesn't really turn off).
I believe this is what you're looking for:
Your transfer rates are going to be about 200kbps (25KBps) with that phonenet adapter.
Have you considered just getting something like a Zip drive and copying them over that way? Or are you a glutton for punishment?