Ok, I just remembered something...
A few months ago I bought this new PSU (the Kingwin Platinum) and when I had everything connected back and the system on, I was playing with one of the fans, which had a cable extension, which had the pins exposed. Guess what happened? I shorted something
I heard a pop and I was sure I'll have a dead mobo. Fortunately, the PSU short circuit protection was up to the task and everything started normally afterwards.
Now, in retrospect, I'm thinking that something gave up and may have something to do with the symptoms described.
I should check the sound card in other computer.