Computer fails to load operating system.

I got a pc that would not boot up. The problem was that it did not detect the hard drive .I was unable to look at it again for a few days , i turned it on this morning and it seems fine. When i first opened the box i noticed that the inside was veryhot. This leads me to believe that there is a problem with the system once it stays on for a extended period of time. If the problem is the tempature , how do i fix the issue?