I would try minimum hardware for boot now and see what happens - one CPU, one stick of RAM etc. Of course it can still be the motherboard that causes this fault but you can rule out almost everything else.
Are you running officially supported components (with Dell HDD included)?
For software side, update your firmware, I don't know how Dell does it but I'm pretty sure they have a "service pack" which checks and updates all the firmwares and drivers to the latest version.
HP uses SPP which is a bootable CD, where you check/select which firmware driver to update.