I just received my Steam Deck OLED 1Tb; the screen is amazing in relation to the LCD version, however I had a problem with the D-PAD not working at all.

I did some testing, and the D-PAD was unresponsive in Gaming Mode, Desktop, and in the BIOS as well, so I figured something wrong with my hardware.

I removed the back panel, and I saw almost instantly that the cable labeled as "DPAD" was disconnected(Right side, just beside the left trigger). Reconnected and now everything is working as intended.

So for short, if something doesn't work hardware wise, contact support, but it may be worth having a look inside and see if anything is disconnected.

Happy Gaming 🎮