seeing as there is NO "upgrade" ( one that is supported by the redhat service contract) between Major
this is a NEW fresh clean install of rhel6.6 ( 6.6 is the current in the 6 series)
did you run the First update
did you have the install dvd auto up[date at time of install
it is now rebooting automatically at various times during the day
or during heavy load ?
how old is this "HP DL180"
a g9 or 6 or ??? what
have you checked the ram ?
what did memtest tell you ?