All PCIe GPU are compatible with all PCIe motherboards and CPUs. Graphics cards are universal now. They have been since AGP was abolished.
It looks like your motherboard has a PCIe x16 slot. (It'll be the black slot closest to the CPU with a locking mechanism.)
HOWEVER - The 300w Power Supply that comes with the P7 1234 will not be able to power a heavy graphics card.
Thankfully you have a TON of options. There are a dozen or more cards that don't require a power connector.
The best three are ~
#3 - The Radeon HD 7750 is the highest card offered that doesn't require a power connector by AMD.
They retail for about $60 to $75 on eBay.
http://www.ebay.com/itm/Sapphire-RADEON-HD-7750-1-GB-PCI-Express-Video-Card-/121688207309?pt=LH_DefaultDomain_0&hash=item1c552eafcd
#2 - There's the GeForce GT 740 from Nvidia. You can find them on eBay for about $75. It'll plug right in without any extra power cables needed.
http://www.ebay.com/itm/GT740-2GD3-Nvidia-Geforce-GT-740-2GB-DDR3-Graphic-Video-Card-Retail-NEW-/271896942637?pt=LH_DefaultDomain_0&hash=item3f4e52182d
#1 - Best card is the GTX 750 ti. This little Maxwell GPU is a MONSTER for it's size and price.
But you must make absolute certain that you get the version that does not require a 6 pin power connector.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814487025
The EVGA model retails for about $150 new. But I've seen them go on eBay for about $100.
These three cards are pretty much top tier for your PC until you build a new one. The Power Supply in your tower is proprietary and can not be replaced or upgraded.
They'll be able to play GTA V, Battlefield 4, Skyrim, Far Cry 4, et cetera, et cetera. And at mostly modest resolutions and even some at 1080. Just make sure you don't crank up MSAA.
Good luck, mate.