My laptop won't reach 1920x1080 which it should?

I bought the laptop Lenovo Ideapad Y580 a year ago and it used to run on the screen resolution 1920x1080 and play games very well on ultra because it was a gaming laptop. Intel core i7, nvidia geforce 660m, 1 tb hard drive, etc. But recently i have reinstalled windows 7 pro 64-bit and as usual put all the drivers and stuff back on, but this time in disply settings it chooses to use the intel graphics 4000 instead of my nvidia one, and it has caused lots of problems. The games don't play without lag usually 15fps and the screen resolution only goes to 1366x768, how can i fix this? I have tried reinstalling drivers, changing in nvidia control panel to high nvidia processor and no luck.