System Requirements for SAPPHIRE VAPOR-X R9 280X 3GB
750 Watt Power Supply is required.
2X150 Watt 8-pin PCI Express power connector is required.
So Fifa 14 doesn't force the card as much as the other games, when you play a much demanding game the graphic card drains all the power from your PSU and the pc freeze
My recommendation is to get one of these PSU EVGA 120-PB-0750-KR http://pcpartpicker.com/part/evga-power-supply-120pb0750kr
or something similar above 750w
You can consider to change from 1x8Gb to 2x4Gb sticks as well