Did you check the bios to see if there is any type of video option, maybe it`s trying to use the integrated video output that comes from the motherboard ( which you still haven`t tried )
Unless you are sure that the "computer tech repair guy" thoroughly tested your motherboard then...
This is the second time this was suggested by AddRAM. Why don't you remove the 690 graphics card and try to get things running on the internal graphics first (remove the GTX690 graphics card). Your monitor appears to have DVI/VGA connectors so you probably need to get hold of a HDMI to DVI connector.
With the Dell monitor check that is either Auto Select or the appropriate input. If you don't have it set properly then you will have problems. On my Dell Ultrasharp monitor you go (Menu>Input Source>Auto Select).
This will take the 690 card out of the issue for the time being and help you see if everything else is ok, especially the motherboard.
The PC is at the shop, no way to check. He seems competent and says the card is fine. He's getting an A2 error. That's all I know at the moment.
I'd also download the motherboard manual if you haven't already.
Motherboards - P8Z77-V DELUXE - ASUS