Blender is lagging

Hi all,
I used to make models in Blender for a long time, and every versions runs fine but now, I have a problem.
I run on Win 7 64-bit with SP1 and my Blender ver. is 2.78 and it is lagging. I was reinstalling my Win because it was so slow but Blender runs perfect. Now I installed Blender on same specs wich is bellow and it starts laggs. I read some forums, I tried to install older NVidia drivers, but it didn’t work, Blender still works slow. Said what else I need to run Blender fine.

Can you help me?

Specs:
Win 7 64-bit with Service Pack 1
i5 - 4440 3.1GHz
NVidia GTX 770 2GB RAM
8GB RAM

Did you are referring while you render? Or lag occurs even without rendering? When exactly happens?
Could you download and try Blender 2.78a?