UEFI is just a new system that replaced BIOS. UEFI is on most motherboards made in the last 2-3 years, and is generally more user friendly, can have many more or more advanced features, and (on the high end) has very fast POST times.
Just press F1 F2 or Del during boot to get into BIOS/UEFI. Once you are in then have it load 'optimized defaults' to reset things, and then exit and reset the computer. If that does not fix the issue then go back in and look for 'init display' or 'first/primary display' and make sure that it is on PCI, there may also be options for the on-board display, and there should be an option to disable the on-board video.
It would be helpful to know what Mobo, CPU, Ram, and other system specs your computer has.