I recently bought the Beyerdynamic DT 990 Pro's 250 Ohm and i loved them and i think they're my favourite headset i've ever used. But whilst watching a video i took them off for a second and put them back on and the audio sounds like it's underwater and quiet. I dont know why this happened and is there anyway to fix this? Also before you tell me to get an Amp, my motherboard support 600 Ohms and the audio quality before was fine and crisp
Is the sound screwed up when you use them with another source? Even if it can't drive 600 ohms properly you should still be able to tell if there are no highs.
Once you know for sure that the problem is the headphones you can contact Beyerdynamic about warranty repair or replacement.