It sounds like you have more than one problem. If the CPU fan worked fine until you installed the drive then something changed and I would examine all connections to make sure that all the plugs are secure and plugged in where they are supposed to be. Also the error you posted indicates a HDD/SSD drive that is failing or has failed. Have you tried pulling the drive you installed in order to see if the error no longer exists?  That very high CPU temp and the fact that the cooler is that hot would indicate a problem with the fan or the cooler is not running properly. The temps should be nowhere near that hot.
So I'm a new Alienware desktop user. I purchased this Alienware Aurora R8 PC from a friend and it was working fine until I opened it up and tried to install a hard drive. When I turned it on it was stuck on = testing CPU fan on the support assist it was stuck on "45 seconds remaining" Then gave me the error, "Error Code 2000-0151 validation 125079. CPU_FAN failed to respond correctly". I DONT think I unplugged any wires or anything I tried to unplug and replug every wire back in to no avail. If anything helps I tried to install an intel driver the same day. Core temp and hwinfo tells me my cpu is 100 degrees anybody know what I might've unplugged or anything? anything helps thanks. btw im on windows 10 64bit and my cooler is a water cooler it gets REALLY hot when I touch the pump it's a corsair h75 aio I think looks like it
Aurora R8, error code 2000-0151 validation 125079