Ok so if it stays in BIOS then the CPU and Memory must be working correctly, you get video ouptut so GPU must be working correctly as well.
Would still go ahead and reseat the GPU and make sure the power plugs are fully inserted.
Also check and make sure that the power cable to every hdd/sdd/dvd drive is properly attached, and make sure the sata cable at both ends (drive and motherbaord) are fully inserted.
If that does not work then disconnect all other drives but your OS drive and see if it boots.
If yes) one of the other drives is bad and start plugging them 1 by 1 until failure.
if no) Reconnect the other drives and disconnect your OS drive, if you boot and get a No Operating System Found error then your OS drive is bad
Also...