Here is the latest RX580 Drivers for your GPU Card: Radeon™ RX 580 Drivers & Support | AMD
Notice that there isn't any Windows 8/8.1 Drivers. That is because AMD doesn't support Windows 8/8.1 anymore thus no updated drivers for that version of Windows.
You will need to upgrade to Windows 10 to get drivers for your GPU card. It still is free.
What does Device Manager show under "Display"? Just your integrated GPU on your AMD APU Processor?
If your GPU card is not recognized than how can you get an output from the card unless you have the cable connected to your motherboard Video outputs which is using your AMD APU integrated graphics.