Can I attach a Video Card to my PC?

[LegendOfBloop]

Processor Type Intel Core i5-4460
Processor Speed 3.2 GHz up to 3.4 GHz
RAM 8 GB (DDR3 SDRAM)
Hard Drive Capacity 1 TB
Hard Drive Speed (Revolutions Per Minute) 7200 RPM
Pre-loaded Operating System Windows 8.1
Graphics Card Intel HD Graphics 4600
Dedicated Graphic Card No
Video Memory 350MHz up to 1100MHz
$599.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16814487028&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=

Processor Cache 6 MB Total Cache)
Available Hard Drive Bays 2 - 3.5 Inches HDD; 1 - 3.5 Inches HDD Available
Available Optical Bays 1 - 5.25 Inches ODD; 0 Available
Available PCIe Slots 1 - PCI-E x16 1 - PCI-E x16 Available
Available PCI Slots 1 - PCI-E x1; 1 - PCI-E x1 Available; 1 - Mini PCI-E 0 - Mini PCI-E Available
Available AGP Slots Not Applicable
Available Memory Slots 0
Removable Storage No
Power Supply 300 W
Energy Star Qualified Yes

Can I put a EVGA GeForce GTX 750 Ti 2GB 128-Bit GDDR5?

 

[i7Baby]

Yes - put it in the pcie x16 slot. As long as it fits in yoyr case. And if you have a good qality 300+W power supply per http://www.geforce.com/hardware/desktop-gpus/geforce-gtx-750-ti/specifications

 

[nostall]

Processor Type Intel Core i5-4460
Processor Speed 3.2 GHz up to 3.4 GHz
RAM 8 GB (DDR3 SDRAM)
Hard Drive Capacity 1 TB
Hard Drive Speed (Revolutions Per Minute) 7200 RPM
Pre-loaded Operating System Windows 8.1
Graphics Card Intel HD Graphics 4600
Dedicated Graphic Card No
Video Memory 350MHz up to 1100MHz
$599.99
http://www.newegg.com/Product/Product.aspx?Item=N82E16814487028&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=

Processor Cache 6 MB Total Cache)
Available Hard Drive Bays 2 - 3.5 Inches HDD; 1 - 3.5 Inches HDD Available
Available Optical Bays 1 - 5.25 Inches ODD; 0 Available
Available PCIe Slots 1 - PCI-E x16 1 - PCI-E x16 Available
Available PCI Slots 1 - PCI-E x1; 1 - PCI-E x1 Available; 1 - Mini PCI-E 0 - Mini PCI-E Available
Available AGP Slots Not Applicable
Available Memory Slots 0
Removable Storage No
Power Supply 300 W
Energy Star Qualified Yes

Can I put a EVGA GeForce GTX 750 Ti 2GB 128-Bit GDDR5?

That particular 750Ti requires a single 6 pin PCIE power connector. You did not specify what brand or model the 300watt power supply is, nor who builds the computer, but I would suspect that that PSU does NOT have a dedicated PCI-E 6 pin lead. I'd be happy if I was wrong.
Also of consideration is if the card will physically fit into the computer. This one doesn't need the auxillary power and should fit into just about any mid tower or larger micro tower case:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814487024&ignorebbr=1