If it doesn't go in easily Back away from it and come back to tech forums for some advice. Be sure to follow the wiring on your motherboard's manufacturers specs in the book they give you when wiring up the power switch. if you don't follow it correctly it could be disaster.
Note on the CPU when installing the CPU make sure these are lined up :
see the indentures on the CPU? well on your motherboard on the socket there will be a little bulge around the perimiter of the CPU tray and those indentures go in it.
The bulges are depicted here.
do you see how the CPU should sit inside the socket? its kinda like a simple puzzle piece.
then after the CPU has been gently set in there you put that silver looknig plate over it and take your tension bar and push it onto the CPU's housing plate.
DO NOT touch the bottom of the CPU.