Gaming computer running slow, it's like-new. Why is kind of slow?

I have recently purchased a gaming computer from newegg.com and it has pretty good specs. I will leave the specs down below. I'm a graphic designer (designing graphics for the gaming community) and that's really all I have been doing. I don't really game much. I have a few games downloaded but not a whole bunch. I will list my games down below. I use this computer daily. I use Photoshop CS6 and Cinema 4D. The only daily things I do on the computer is use those two programs and use Twitter. Nothing else.

Games I have downloaded:

Combat Arms (FPS GAME)
League of Leagends (MMO GAME)
Counter Strike CS: GO (FPS GAME)
Terraria (N/A)
Minecraft (N/A

Like I said, I rarely play those games. Hardly ever really.

My question is what is wrong? How do I check the reason why it's running slow? If I can buy a part to replace, what should I buy to better my performance? I know a new processor would probably work, but I shouldn't need any more replacements as I purchased this pc about 7 months ago.

When I got my PC, it loaded everything with such swiftness. I can watch movies without it buffering out skipping. Now I can't even watch a 360p movie without it buffering and stuttering through the movie.

Here is my computer: http://www.newegg.com/...6883229619

My internet speed is flawless
Ping:11
Download:140mbps
Upload:15mbps

That video card is ultra low end, that would affect the gaming but as for the other stuff. Just do the usual virus checks and stuff, registry cleaners, etc. If that doesn't work try reinstalling windows or something. Id bet its a software issue not a hardware one

must be nice having speeds like that i still get like 10 mbps at most

With the programs your running… I'd consider adding another 4 gig of ram… It may be that between the OS and what ever program or programs your running at the same your ram resources may be maxed out…

As for movies buffering… Well that can happen several ways… Your processor is maxed out ( are you doing things with other programs while trying to watch a movie / video )… Or your internet connection is like really slow…