I would check the motherboard for bad caps:https://www.google.com/search?hl=en&sit ... ZpZNdCvIf0
If you have any caps like you see in the images, bulging split and leaking the motherboard has to be repaired or replaced. Some times you will have bad caps in the psu as well, I would take a peek inside, if you can.
Find the manufactures name of your hard drive and go to its site, download the ISO for testing the hard drive and make a cd to do so. There are two tests, quick and long I always run both even if the first one says the drive is ok. I have found in the past the long test will find problems where the short test will not.
To eliminate any problems with the os download a Linux Live cd and see if it will boot right up to it. if it does the pc is probably ok but windows may not be.
Hope this helps a little bit....