I have a 2 year old A855 that had been suffering from a bad digitizer. (dead spots, random key pressing, ect)
I decided to go ahead and replace the digitizer myself so I ordered one off Amazon. I installed it and the phone wouldn't power on, just a slight brightening of the screen when power button was pressed.
Thinking I may have done something wrong, I disassembled the phone again and checked all the connections. Reassembled and the same thing, just a slight brightening of the screen. About to give up after several battery pulls/re-starts and whala! On it comes! Tested it out and the new digitizer was working great! I used the phone all day and had to do one battery pull/restart at one point but it came right back on. After an extended phone call I went to hang up and the screen was dark and wouldn't wake up. Pulled battery again and this time back to the slight brightening of screen and nothing more. I have tried many more battery pulls, holding x and powering, ect. all with no effect.
Any suggestions or is it time for a new phone?