I was fixing a computer in the house the other day running windows 8.1, the problem was it loaded up to the windows logo and just stayed there idenfinatly, I asked my Dad what he had recently done on the computer and he said he had run a registry cleaner program (so i assumed it had removed a critical component from the windows registry). So I put in the windows 8.1 dvd and tried a OS repair but it failed with an error so next I tried a system restore and that failed too with and error, After messing around with it for a bit I got tired of the problem and decided I would just reformat the machine and start fresh. After reformating the computer everything was running fine but I noticed the machine was running a little slow and would slow right down when trying to open a program, I restarted the computer though and it seemed to be okay so I dismissed it as nothing to worry about. After a couple of days though the computer back to starting up and going to the windows logo and it sits there indefinatly again. So i know its nothing related to the OS now but I was wondering what could cause this problem, could a hardware component be failing and if so which is most likely to be doing so?