Question Kind of good components,super slow system?

[Kraspeto]

So we build our frend a budget friendly PC. For low games such as LoL or Paladins.And he's getting strange non consistent lag while playing.It's not like it lags all the time,just on certain moment lags hard.And im asking if someone could tell what could possibly be the problem.
Thermal paste is changed.HDD is new.Drivers are up to date.
Specs:
AMD FX-6300
MOBO: ASRock 960GC GS FX
RAM 8 gb Sesame 1600mhz
PSU DEEP COOL dn450 80plus
MSI GTX 960 4 GB GDDR5
HDD Seagate Barracuda 3.5 1TB 7200rpm(ST1000DM010).
Monitor is Samsung s24r350fhu.

 

[rgd1101]

check cpu temp?
ram and hdd usage during the game?