To begin with go here and download the ROM of your country/region
Secondly download smartflash and drivers from here and install them
Now run SmartFlashTool_P990.exe
Turn the phone off,remove the battery and connect the phone to pc via usb while holding down the vol.down button.
Now you should be able to see the software upgrade screen, and COM port of smartflash will change automatically.
Now in smart flash select "ROM Copy D/L"
Make sure that "Normal Mode" is checked and "Erase Cal" is NOT checked
In AP Bin click browser and select the (BIN) file
In CP Bin click browser and select the (FLS) file
Click start, sit back and wait
I'll try to remember next time that I return to stock rom record it and upload it
Here is the video I said i would record