You will need to perform a 'Clean Installation'
In order to do this, you will need to locate the AMD Installation Directory.
Typically this will be C:\AMD\[Driver Version]
Go into [Driver Version]\Bin64 … it really doesn't matter which, and run AMDCleanupUtility.exe
This will take a few minutes, then ask you to Reboot your Computer.
Once you do so, ALL AMD Related Drivers will have been Purged from Windows.
Delete the AMD Directory
Then you can go to the Driver area of the AMD Website, and Install the current "Recommended" (which should be Version 18.9.0)
That should resolve any issues you were having.
As a further note, if you're using an AMD Platform (i.e. Ryzen, FX, A-Series CPU) then I'd recommend installing the Chipset Drivers as well, as annoyingly this doesn't automatically happen with the AMD Installer as it ALWAYS defaults to Graphics Driver Installation.
In fact be sure when you install Chipset Drivers that you DO NOT click on "Recommended", but instead click on "Local" because otherwise it'll just install Graphics Drivers again.