First make sure you have the latest/greatest drivers and not just what shipped with the new card.
Then do a Windows Update and get all the goodies necessary from there including any Service Packs.
Clean all intakes and exhaust areas on the PC. They get gunked up pretty easily. Don’t forget the power supply intakes/exhaust.
If it keeps crashing know that turning your GPU fans on high only helps some. With that card those fans will be pushing hot air from the card mostly into the case of the PC and not exhaust it. As such you could be raising the internal temp of the case dramatically. This can then cause either your video card or CPU to overheat and shutdown the PC.
As a test try running a game that crashes the PC on the lowest graphics settings possible. Hopefully this will not stress the card and cause it to heat up. If the game continues without crashing then it is the case temp that is causing problems. (You can also download tools to monitor CPU/GPU temps and log the results…play for ten minutes or so and see if that temp is marching up.)
If this is the problem you need better case cooling. That may be as simple as some new fans or may require a new case depending on how things are currently setup. Cleaning up a rat’s nest of wires can also help some. Do some cable management and get them neatly bundled and out of the way to aid in clean air flow to the important components. If possible, you may consider moving the video card to a slot further from the CPU.
If the CPU is overheating a new heat sink/fan might be in order. The stock fan shipped with Intel CPUs is rather crappy. Rarely will a store bought PC have a nice heat sink/fan on it (one way they keep prices down). If they did replace the stock heat sink with a nice one the PC will likely be at a premium price and they’ll advertise that they did that. If you look inside the case the stock heat sink looks like this.
Case cooling, especially air cooling, for a powerful gaming rig takes a fair bit of attention. You can end up with a PC that sounds like a jet plane taking off with all the fans. It is possible (I do it currently) with a good case and a good setup to have a relatively silent PC with sufficient air cooling but I had to work at it to get it setup that way. Only occasionally will my GPU ramp up fans speed and even then it is not very noticeable.
ETA: Double check your power supply has sufficient power to run that card and that all power connectors the card needs are connected (often they need more than the slot provides and needs its own connection to the power supply).