The shutdowns is the Thermal Protection in the BIOS shutting down your system when your GPU hits 114C. I suggest a thermal repaste for the GPU. I also suggest an update to BIOS 211 and updating the vBIOS to the GSOD Fix Beta if you haven't already.
If this is beyond your expertise, I suggest calling Asus Customer Support for an RMA, and arranging a repaste and BIOS/vBIOS flash at a local ASP location. You can get a list of locations here:
http://promos.asus.com/US/ASUS_NB_Warranty/NB_ANSP/index.htmlThere are several stickies in this forum that provide more information.
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