If it happened only once I wouldn't worry, the GPU forced the PC to shut down to protect itself it's normal behavior, if you have benchmarks you run often and know the scores/average framerate run them and see if you get the usual normal performance just to make sure everything's okay.
Sapphire Radeon R9 290 4GB Tri-X
Seagate 2TB 2000DM001
Seagate 3TB 3000DM001
Windows 7 64bit
Microsoft Digital Media Keyboard 3000
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