One bad lead can cause a computer to continue on a cycle or to shutdown or fail to detect your hard drive
Test the leads that attach to your ((hard drive from the motherboard)) or replace all the leads that attach to your hard drive including electrical extensions + IDE,SATA and the ones that attach from your ((motherboard to hard drive))
make sure all leads that are attached to your drives dvd\cd 3 1/2 inch floppy have secure connections and are not faulty even the electrical extensions or just replace them they are probably old and faulty a computer needs its connections to have an end so any faulty leads will end up with a computer error


hope this helps