Hi all
Im new here so please be gentle ,
 
Im having a few problems with my card , EVGA 750 ti SC
I have been trying to over clock it a little bit , and all tho a run benchmarks (heaven on ultra ) for 30mins or so and it seems stable , no crashers at all, no driver stop working , all is fine.
but while playing a game (tomb raider) i can play for about an hour and then it crash's "driver stop's working" and reverts back to default
 
now im totally new to PC gaming and overclocking anything ,
but if don't ask then i won't know ,
 
so i have set the card to:
GPU clock offset +85 >which can reach 1404
MEM clock off set +20 which sits around 1156
no extra voltage , as i have read it is bad for the card and shortens the life of it ,
the temp of the card doesn't get any higher than 50'c
FAN speed is at 40%
 
what can i do to ,so that the card is over clocked and is stable for more than an hour ? please
 
few specs
i5 3470
W7
8gb ram corsair vengeance
asrock h61m-dgs
500w pcu

Thank you Scarlet tech ,
i will try adding more memory ,
would adding  voltage help in the matter , or should i keep away from adding that ?

Ideally, you'd want to push both as high as possible.  With newer cards, performance tends to scale better with memory clock gains more so than gpu clock gains.  Since you want to overclock the gpu clock and memory separately, start with getting your maximum memory clock stable first, and then push the gpu clock higher.  
 
More voltage can help with a higher overclock, but too much voltage can also make the gpu unstable.  Start first by seeing what you can get just by raising the power target to the max, and then raise the voltage a little bit from there, as you continue pushing the gpu clock.