I have had the exact same original problem with 2 different phones.
Problem: Turn on, green light stays on for a second or two and then switches off. Both times the problem was the main ribbon cable.
Solution: Open up the phone and reconnect the main ribbon connector that runs between the two halves of the phone. Hope this helps someone!
Instructions: - Simply remove battery cover
- Remove battery
- Unscrew the two screws at the bottom of phone that was under the battery cover
- Unclip the back phone casing. I used an old credit card and wedges it on the inside of the casings and ran it around unclipping all the clips.
- Unscrew the (clear) speaker assembly
- Slide the phone 3/4 open, lift the mainboard and gain access to the ribbon cable.
- Simply ease it off and clip it back on again.
Note: I had to refit the connector around 5 times to get it right on both occasions. The pins are very fine. I found pressing the ribbon side down first helped.
Good luck!
Edited by Tris, 25 January 2009 - 05:37 PM.