When everything is plugged in, my computer shuts down after 4-5 seconds. I unplugged the HDD and now the computer stays on. Is this a problem with the HDD or something else?
Sounds like a problem with the HDD. The only way to be 100% sure is to replace it with a known good working HDD and load Windows and see what happens. If it loads and works fine then it's the HDD.
Im pretty sure if you fried this HDD your better off getting a green drive that doesnt run the whole time and will not burn out when your not using it but there could be multiple causes of your problem