cannot get my 7850k apu to switch to my hd 7770 ?

[a39232]

I have tried everything I could think of (and that was quite a lot) I even tried disabling the onboard gpu in BIOS and putting the HD 7770 in and it still would not accept it. Had to clear the CMOS got it booted up and tried some more. I tried it in my moms computer (FX-4300) no problems however under mange it listed it as (R7 200 graphics) so I was puzzled on how that happened. please help.

MotherboardGA-F2A78M-HD2 (rev. 3.0)

http://www.gigabyte.com/products/product-page.aspx?pid=4909#ov
APU: 7850k

 

[Calvin7]

Your power supply may not have enough watts to start the HD 7770 card.

 

[a39232]

Your power supply may not have enough watts to start the HD 7770 card.

the computer I used to test had a 400 watt psu with a Athlon 7550 and it worked fine the 7850k can power up the fan so I assume it is on.