Hello there
As the title says, recently I've noticed my old computer is encountering some strange lag spikes out of nowere. The lag comes after five to ten minutes of playing ANY game. (From Battlefield 4 to Minecraft). The drivers are not problem as I've updated them some days ago. Also, the dust inside a PC just got cleaned two days ago. (Lags are shorter after the cleaning but still they come from time to time).
Windows was re-installed one month ago, yet the lag spikes are still here. Also, my memory is not the problem as only 50GB is used from 800GB total memory.
What may be a problem?
My configuration:

(Yup, I know that the configuration is a bit outdated but it's my secondary PC that is not being used for more than YouTube, Facebook, GTA-SA and League of Legends, so please refrain from posting "omg bad config", "gez new pc omg" and such unnecessary comments.)