I agree… the issue is nothing about V/G-Sync… it is the “no fps Limit” and in case a PC crash with “no fps limit” and works fine “with a limit”, it is usually a hardware issue ( mainly over-heating ).
We can also see that, if the OP set a “not sufficent” limit, then he can play some-minutes - again this point to overheating.
PS: and also V-Sync must enabled if G-Sync will be used