Ok, I have checked the "phisical" manual. So debug LED code number 15 means "Pre-memory North-Bridge initialization is started". Hmm, it's not hepful with the problem of my sound card. Any ideas, what can be with it? Without card mortherboard starts properly...
Welp, my sound card is Audiotrak Prodigy HD2 Advanced DE and it was nice, because of very strong and high quality signal in headphones output. It seems that the card is dead Unfortunatelly I bought it with short limited warranty period.
Realtek is not a heap of trash, but the output signal is noticeable worse.