Do you have onboard graphics or a seperate graphics card (like a PCI or AGP graphics card...?
If you don't know, then if your monitor is plugged into a VGA port on the I/O bracket on the back of the PC (along with other ports like USB, serial and ethernet etc...) then it's onboard.
If the monitor is plugged into a port at the bottom of your PC underneath the I/O bracket on the back, then you can tell if it's plugged into a PCI or AGP card.
|Desktop PC| |Macbook Air 13" (Mid 2013)|
|Windows 8.1 Pro (x64)| |AMD FX 4100 Black Edition 3.6 GHz @ 4.0 GHz OC| |Arctic Cooling Freezer 13 PRO| |Gigabyte Nvidia GeForce GTX 560 Super Overclock 1GB| |ASUS M5A78L-M/USB3 Motherboard| |Samsung 840 Pro 256GB SSD SATA III HDD| |Kingston HyperX 8GB PC3-14900 DDR3-1866| |OCZ ModXStream Pro 700W Modular PSU| |NZXT Vulcan Micro ATX Case|