This happens during 3 activities, sometimes just after startup, sometimes while playing and sometimes when loading things. Monitor goes black first, sound dies after around 5 seconds, however, the PC components are running. Somebody mentioned that the power supply could be an issue. Note: I built this PC half a year ago, everything is brand new.
Edit: Everything is suddenly loading very slowly, which made my PC crash again. After I restarted it, it is still slower.
Thank you in advance.