I bought a non-working G15 off of Ebay about a month ago in hopes of easily fixing it, the display didn't work, so I replaced the display and it still doesn't work. After that, I removed the mainboard and cleaned it with rubbing alcohol hoping that the board's corrosion was causing it; Nope. This time, it wouldn't turn on unless I held the power button and the display still didn't work. I took it apart again and reseated the internal CMOS battery and this time when I tried to turn it on, nothing happened. I ordered a new mainboard and put it in and it still doesn't do anything when I try to turn it on. I'm thinking the flash board may be dead or the power button somehow doesn't work. Thoughts? I'm gonna pull all of my hair out.
The list of what was originally wrong in addition to what the new symptoms are is pretty long. (display, various connectors, motherboard, battery box, DC board, etc, etc) I think you got the best advice, cut your losses now and let that camera R.I.P.
The upside is you did get what you paid for on eBay, a non-working camera.