make sure everything is disconnected when booting up as far pen drives, memory cards, external hard drives....
i had a similar thing happen and it was a shorted pen drive that didnt let it boot.
did you try safe mode ? shutting off un-necassary drivers to boot up
i had a similar thing happen and it was a shorted pen drive that didnt let it boot.
did you try safe mode ? shutting off un-necassary drivers to boot up