If you had another Pci-e graphics card in the system before you fitted the new R9 390X card.
Did you remove the video driver used with the old graphics card if the case for that card before you took it out and put the R9 card in the Pci-e graphics card slot of your motherboard.
If the existing card was a different model version of a Ati gpu, or and Nvidia based card with a Nvidia gpu.
You must remove the old video driver for the old Pci-e based graphics card first of all.
Or the result is you get really bad frame rates out of the new R9 390X graphics card GTR22.
Download and install this program if the case,run it , and use the options to remove both Nvidia based graphics drivers
And any Ati video drivers.
http://www.guru3d.com/files-details/display-driver-uninstaller-download.html
Then download the latest drivers from www.Amd.com for your model of R9 graphics card you currently have.
Once done and the latest video driver is installed.
Try a game and see if the FPS have improved.