Giving pre-built motherboard models doesn't usually help. It would help to know what CPU you have, or even the model of Acer computer you have. The '31' implies a Core 2 Duo CPU. If that's the case I'd stick to GTX 750 Ti and earlier if you like Nvidia. That assures maximum compatibility. A lot depends on your power supply too.
Giving pre-built motherboard models doesn't usually help. It would help to know what CPU you have, or even the model of Acer computer you have. The '31' implies a Core 2 Duo CPU. If that's the case I'd stick to GTX 750 Ti and earlier if you like Nvidia. That assures maximum compatibility. A lot depends on your power supply too.