http://www.motherboardpoint.com/t57621-boot-failed-at-checkpoint-ithr-this-solution-works-for-me.html

Hi Adam

I had this same problem with my D 8400 about a year ago i took the battery out

let it set for a while after unplugging the power cord and pressing the power button

for a few seconds !!

Putting the  battery back in it would boot with no problem

but it did it again after about a month so i replaced the battery this time and

never had a problem after that so i would just replace the battery now!!

 Good Luck !