Usually if you have a faulty hard drive it will only go pass the boot stage then end up saying that it can't find an OS.
He can load the operating system but it crashes as soon as it fully loads meaning something is wrong with the drivers or software, not the hardware.

when my ssd failed, it would try loading the OS and jump straight to a blue screen, rather than saying it can't find an OS

also, just because his system manages to load up the OS doesn't mean that it completely singles it down to a software or driver issue, even though that is the likely scenario which is why i'm telling him to wipe his hdd and re-install his OS.

iIluminati: if you're still having issues after re-installing/wiping your hard drive, my only guess that it's hardware related, specifically your hard drive