Computer slowdown, how do I find the problem?

hi. my new asus notebook got slow down problem. My asus is 6 months old but I rarely use it, so it still new.

Its often randomly slow down, and ocasionally crashes (not responding). but in another day it could suddenly work fine. 

So far I tried to download trial version of norton internet security and run a full scan, there's some "threat", fixed, but slow down problem still persist

I then tried deffrager software but fragmented segment is less than 4% so I decided not to defrag it

I then tried ccleaner and clean some junks but slow down problem still happen randomly

what to do next?



Gatekeeper Edit: moved.

- The_gh0stm4n