New set up with Aorus B360 Gaming 3 Wifi Mobo won't boot when using older GPU

[rowan_archbald]

Hi,
I would like to use an older GPU with my new set up until such a time as i can get a new GPU. I am having POST issues when the card is installed and connected, but no issues booting etc when the card is not installed - so the GPU seems to be the culprit. The old GPU is Radeon R7 260x and the new hardware/setup is:
Mobo: Aorus B360 Gaming 3 Wifi
RAM: 16gb corsair vengeance 2666
CPU: Intel i5-8400
OS: Windows 10

I saw elsewhere that the different PCIe slots might have something to do with it, but i have tested two of the three slots and it didn't work for either - the third slot is not able to be used with this card as it is too close to the bottom of the case for it to be installed.
I am a bit of an amateur with all of this, and this is the first time I have replaced a mobo and CPU so please explain it simply!
Thanks!

 

[cin19]

What PSU did you have?

 

[rowan_archbald]

I'll have to check brand etc when I am home, but I am reusing my 500w supply which was working in the previous machine, and from what I have checked online should be powerful enough for this new build.

 

[cin19]

Also if the boot device is from the previous machine with the OS too, do you use the DDU to uninstall the GPU driver first? because, sometime, the previous GPU driver will cause problem too.
DDU https://www.guru3d.com/files_details/display_driver_uninstaller_download.html

 

[rowan_archbald]

I didn't do that, but i did format the SSD (only have the one drive) and a fresh install of windows 10. Would formatting the drive be enough to sort that or is it likely that previous drivers etc might be causing issues still?