For some reason, on these Optiplex machines (with on-board video) that are usually used in an office with NO dedicated video-card ... they are sometimes stubborn about detecting a dedicated GPU when finally asked.

See:

https://www.dell.com/community/Optiplex-Desktops/9010-hangs-during-boot-with-Radeon-R7-250/m-p/6166866#M28548

The BIOS cant detect the cards either. Maybe its a hardware issue with the motherboard?

Thanks for the reply, will see if that would solve the problem.

im having  same problem with my 7020 mobo but I'm trying to use a rx 570 with it but  I tried a gt 610 also and that didn't work I was going to get a new motherboard but something happened and now I don't got the money for it I went through the bios couldn't find anything that fixed it and the few times it was detected was the bios saying I cant have integrated plugged in and the discrete gpu  and when I restarted like it said it didn't detect the gpu anymore I only got into windows with it detected once and it wouldn't output tho I could see it in device manager

I am having same issue please help 

Do these steps or just keep "trying things" until it starts working.

Be carefull not to damage anything in process (ie, always dissipate flea-power, etc.)

https://www.dell.com/community/Optiplex-Desktops/9010-hangs-during-boot-with-Radeon-R7-250/m-p/6166866#M28548

"The only thing I see in device manager is my Integrated Graphics adapter."

My guess is you have not installed your drivers. I can infer that based on the fact you can see device manager which is not accessible on a computer with actual hardware problems.

http://us.download.nvidia.com/Windows/327.23/327.23-desktop-win8-win7-winvista-64bit-english-whql.exe

I had the same issue on my 7010 MT with an rx 570. Apparently, the card had been used for mining. Thankfully, it worked by flashing amdclockpatcher. I pray this helps!

Right, so, you need to install GPU drivers this makes your computer detect it