Problemas con dual graphic con A8-7650k + XFX R7 240 2gb ddr3

Hello,
Did you leveraged the bios options of your motherboard. Did you updated your bios, APU and GPU drivers?
From what i remember there are specific options to set up to allow the dual graphics to works.
Looking your motherboard manual, here what is reported:

Step 1. Please keep the default UEFI setting of “Dual Graphics“ option on [Auto].

Step 2. Install one AMD RADEON PCI Express graphics card to PCIE1 slot.

Step 3. Connect the monitor cable to the onboard VGA port. Please be noted that

the current VGA driver / VBIOS can allow Dual Graphics output from on

-board display only. For any future update, please refer to our website for

further information. 

Step 4. Boot into OS. Please remove the AMD driver if you have any VGA driver

installed in your system.

Step 5.  Install the onboard VGA driver from our support CD to your system for

both the onboard VGA and the discrete graphics card.

Step 6. Restart your computer. Right-click the desktop. Click “AMD VISION

Engine Control Center” to enter AMD VISION Engine Control Center.

Step 7. You can also click “AMD VISION Engine Control Center” on your

Windows® taskbar to enter AMD VISION Engine Control Center.

Step 8. In AMD VISION Engine Control Center, please choose “Performance”.

Step 9. Click “Enable CrossFire” and click “Apply“ to save your change.

Step 10. Reboot your system. Then you can freely enjoy the benefit of Dual

Graphics feature. 

If this do not work, you should maybe inquire further into the bios options, it seems there is maybe a specific set of options to set up in order to get it work properly.
You can check this video as exemple: How to setup AMD dual graphics (hybrid crossfire) - YouTube