As your warning message says 'due to thermal event',
First thing I'd do is check its clean inside, I know its not an old unit, but depending on where it lives it may be a dust haven, best to make sure your not clogged up already hehe,
secondly, how many fans are in there? might need more fitted
and it may also be an issue that the heatsink on the psu is causing,
give us some feedback, and pictures of the unit if possible please.
If the problem does lie with the graphics card its still their duty to resolve the issue, (assuming it was fitted as part of the original sale and not put in by you afterwards)
you bought what you expected to be a fully functioning system from a reputable? vendor,
great job so far in that they've identified (hopefully) the issue,
time to carry the good service on by making sure your rig works as it should, I'm not sure what your region has as consumer protection, but in the uk we have laws to try and protect you in circumstances like this,
let me know how you get on man.