Issue with my OS

Hi, I am having a huge problem with my OS.
My specs are : core i7 4771 , 16 GB DDR 3 , GTX 760 , 4 TB HDD , 256 GB SSD dedicated for Windows installation.
I have a legit copy of windows 8 . I upgraded it to 8.1 from store.
Now my OS is super slow. I have a dual monitor setup. For example if I am watching a blu ray movie on VLC or Media Player Classic and I open Chrome on the other monitor , the movie lags like hell and I get buzzing high pitch sound from the speakers due to the lag. It continues to lag .
I tried to open other browsers while watching movie but same thing. I cannot do more than one thing at a time but I think my cpu is capable of doing it.
The softwares which are installed in the system are CCleaner, Super AntiSpyware, Avast Internet Security .
I just formatted the PC approx a week ago. Also when I am trying to open Chrome, it takes like 2-3 seconds to open. Any application I try to open , takes some 2-3 seconds to open. Its like super slow like a pentium 3 pc .
Also my mouse sometimes lag while I am trying to move the cursor. It literally teleports from one corner to another.
Anything I am trying to do is super slow.

Can anyone tell what is the problem and how to solve ?

Since you updated to windows 8.1 - verify all your drivers are for Windows 8.1

Not all drivers for 8 work in 8.1

If you are doing these tasks from the Metro/Start screen, yes you will have issues. If it is happening in the Desktop, then you need to look at running tasks in Task Manager and find out what is spiking the CPU.

Resource Monitor can help pinpoint the causes of CPU spikes , too.