I have dual boot (Ubuntu and Win7) on my computer for 2 months. My computer is Sony VAIO VPCF22S1E. It has i7 CPU and 8GB RAM

There is a weird slowness for a few months on Windows 7 OS. While using Ubuntu there isn't any slowness. But while i'm using Win 7 there is slowness.
Nod32 installed on my computer and i'm scanning my all devices on in-depth scan mode and there isn't any virus etc.
But on every Windows 7 startup i'm getting an "hKIow... (meanless chars) has stopped working" error. I have googled name of application (hKIow...) but there isn't any result.
Also i'm defragmenting my harddisk regularly .
I don't want to format my computer.
How you any idea for me ?