Lagg ENDAST i CS:GO

Hallå!

En kompis har problem med fryslagg och stuttering i CS:GO och jag tänkte att ni här har bättre koll på burkar och fps än dom på steams egna forum. Postar hans inlägg nedan och ber om ursäkt för att jag inte orkat översätta.

I recently bought a new gaming computer and a friend of mine helped me build it.

Here's what I have;

Kingston SSDNow V300 240GB 2.5" OEM
MSI GeForce GTX 960 2GB
Corsair Vengeance DDR 1600MHz 8GB CL9
Intel Core i5-4690K, Socket-LGA1150
MSI B85M-E45, Socket-1150

Dell monitor 60hz VGA connected.

My problem:

My computer lags/stutter for like a millisecond. FPS drops from 300 to 250 every now and then. Just looking at another player can be enough for it to drop, and since my computer is brand new this shouldn't happen. I'm not that bright at fixing tech stuffs but I've tried my best.

My attempts and thoughts:

Reinstalled Nvidia driver
Installed an earlier Nvidia driver (didnt work)
Tried all kind of settings to set in the console, such as;-thread 4, -high, -novid, rate 128000 etc
Been looking around a lot on the internet and tried their way
Reinstalled CS:GO several times
Managed the settings in the Nvidia control to the most fit for gaming. Vsync off etc.
Downloaded Battlefield 4 just to check if it remained, it didnt.
My roommate's computer doesnt have any lag at all, which means we can exclude the network.
Can it be something with my audio driver?

Tack.