One bad lead can cause a computer to continue on a cycle or to shutdown or fail to detect your hard drive boot up

test all leads that attach to your hard drive including electrical extensions SATA

the leads from your ((motherboard to your hard drive)) make sure they have a secure connection and are not faulty or just replace them they could be faulty

make sure all leads that are attached to your drives dvd\cd have secure connections and are not faulty or just replace them they could be faulty ?

even something as small as an electrical extension or a faulty fan lead can cause this problem computer needs all of the data and power to travel through every working device and to have an end for a computer to be able work properly

a motherboard and a hard drive any leads between them will fail before your motherboard or your hard drive check all electrical extensions make sure they are securely seated even the cd/dvd drives need to have current go through make sure these devices are working

also check your computer ram modules and cmos battery to make sure they are securely seated and the battery has plenty of charge Cmos battery on some motherboards are soldered in

hope this helps you