I am having the EXACT same issue. X5L would not boot past the initial "iAudio" Screen. It would interface normally with the computer via USB, and it would charge normally. However, when I went to power up, it just sat on the start screen for 4-5 minutes then shut off.
A friend recommended I try Rockbox and now everything seems to work, except I get no sound at all out of it. I have checked and adjusted every setting I thought might be relevant. No sound from the radio, not from MP3s.