PC running kinda slow

So I have a PC, with Windows 7 Ultimate x64 installed just yesterday. It is running sluggerish if I can say so.
I will try to explain now. When I'm on YouTube, it sometimes freezes to the point that I can see the mouse pointer moving, but I can't click on anything for about 5 seconds. This occurs after I enter and exit fullscreen mode as well. Next thing is that Twitch videos lag. I know for sure that it is not a problem with my ISP.
Sometimes, even when I'm not in browser, it lags. I don't know how to explain, it just feels like it's not fluid. It's like I'm using a pc from 2005.
An Intel i5 4460 with 8GB RAM and R9 280x video card shouldn't have any problem doing this basic things. What I'm trying to ask here is how to fix all those problems and optimize my PC to run at it's potential. I need full details on why it does the things it does and how to fix them, to fully optimize my PC. If you guys need more info, please ask.

Thank you! :)

As you said you only installed it yesterday, its more than likely that its downloading the 200+ updates, that uses a lot of bandwidth, give it a good day for those and check back in 3/4 if its still a problem.

Roy

torchwood said:

As you said you only installed it yesterday, its more than likely that its downloading the 200+ updates, that uses a lot of bandwidth, give it a good day for those and check back in 3/4 if its still a problem.

Roy

Well the thing is, I reinstalled windows because I had the same problems before. It's not from the bandwidth.

And I was talking about the PC in general as well. It sometimes lag or not run fluidly even when I browse through folders.

AddRAM said:

I would download your own iso file and burn to dvd at no faster then x4 speed or reinstall the iso file on the usb stick again.

Do you have a genuine windows 7 Ultimate activation key ?

Did you build the PC ?

Or is it store bought, does it have a COA on it ?

It came preactivated. I built my PC.

AddRAM said:

There`s no such thing as pre activated, you will need a genuine key, in order for us to help you.

Well I need help to optimize my drivers I guess, and maybe clean my PC from unwanted files that may slow it down. How does having a key help you?