|You probably don't have to do an XP Repair installation.|
Check out the AMD web site and see if there is a Processor driver available for this cpu you can install.
Did you check the cpu compatibility list for the mboard model?
"msi X790 mobo"
It may have an X790 chipset, but there's no such MSI mboard model. Which model is it ?
The model, sometimes the make, of a mboard in a generic desktop system is usually printed on the mboard's surface in obvious larger characters, often between the slots.
Unless the instructions for installing a device tell you otherwise.......
You DO NOT install drivers for a device while booting into Windows, if the software for the device has not been installed yet - when Windows detects a generic device while booting, you allow it to search for drivers, it doesn't find any, and it wants you to show it the location of the drivers - CANCEL that, continue on to the desktop, and install the software for the device using the proper installation from a CD or the proper installation file that you downloaded from the web.
If you DID install drivers that way, go to Control Panel - Classic View - Add/Remove Programs and Un-install the software you installed, reboot, DO NOT install drivers while booting, and install the software the right way !