OPen up the side and looksee what the motherboard says on it and if you go to About this Mac and clicky more info it will tell you how much Ram, CPU speed and what your GPU is. It would be nice to know the makes of it all to figure out how to help you.
On my iMac, or any Mac with a Mac key board, the F14 and F15 keys are display brightness up and down. And your probably using a Windows key board so those keys are your Home and End buttons, in that case I don't know lol.