new GPU now no bootable devices

[vegeto1988]

I was running with a GTX 770 and upgraded to a GTX 1070 TI.

Booted the pc and got "Select proper bootable device" error.

I was using a 700W PSU, but previously noticed that when I had more then 2 USB devices connected there were more errors with the USB devices (Wireless headset for example would lose connection, or external HD would need to be reset). I assumed that perhaps it was a PSU issue so I ran around town and found the biggest PSU I could, a nice 750W (not a big jump but was best I could get)

Installed it and again same issue. Then the PC stopped detecting any of the 2 HD connected (a 120GB SSD and 1TB HD) and say no bootable devices found at all. Checked all cabling everything is connected fully and back to "Select Proper Bootable Device"

What is the next step to fix this?

Original Computer Specs:
prebuilt ASUS ROG - CG8580

Intel Core i7-3770/ 3.5 GHz
16 GB Ram (4x 4GB DDR3)
Xonar Phoebus Sound Card
upgraded to GTX 770 from factory GTX 680
700W PSU

 

[vegeto1988]

update: Twice I went to start the PC and it kept turning itself off as it was starting up repeatedly but eventually was able to start up but again not able to boot.