Screen keeps going black intermittently

I have a HTPC which I have connected to my Smart TV via Marantz receiver with HDMI cables.

Recently, when watching media from the HTPC, I have noticed that the screen goes black for 1 or 2 seconds, but the audio is unaffected. When watching ordinary TV or Netflix, the video and audio has no issues at all. The media is HD, but not anything like UHD 4K

Would anyone know what causes this? I have tried reseating the HTPC graphics card, checked the HDMI connections. Reading online points me to either the graphics card or HDMI cables but before I start replacing these, I figured I would ask here first.