What are you doing with the PC? Because if you are just playing games theres no need to OC it would just shorten the lifespan of your CPU. Also sounds like you need to turn up to voltage to make your OC stable.
Go into your bios and find the video output option. It can be named many different things but you should have an option to set the primary to igpu or pci. Any lights turn on (like the two power lights)? Do the fans on the card spin up? Make sure the card is seated properly and have both PCI-E...