After years (!) with an odd problem to a customer I finally got over this post which has exactly the same problem that I was facing:
The problem was on a warm-boot the server would just freeze in the bios during the power cycle. No error messages in the ILO-log either.
It seems like actually the problem was the KVM (keyboard,video,mouse) which was not 100% compatible with HP i guess.. Really weird..
That also bring my attention that I can actually cause a bluescreen on a HP Proliant DL 380 G7 if I connect a HP USB-keyboard on the front USB… that necessary a thing that is well documented in the usermanual…