OK. Well it needs BIOS 0609 to support that CPU
Core i7-4790K (4.0Ghz, 4C, HT, L3:8M, HD Graphic, 88W, rev.C0) ALL 0609
Since this mobo supports USB BIOS flashback download the latest BIOS
http://dlcdnet.asus.com/pub/ASUS/mb/LGA1150/MAXIMUS-VII-HERO/MAXIMUS-VII-HERO-ASUS-2012.zip
Dont worry if the system isnt running, flashback just needs a PSU.
Extract it, rename the rom file to whatever the manual says you have to rename it to
Copy it to a flash drive
Put it in whatever USB port flashback uses, press the button on the back. Wait for it to finish
Also check that the SATA power and data cable are connected.