I stopped playing D2 when Blizz started deleting accounts for only a month of inactivity.
I was stuck in nightmare as well, as I was forced to fight a sub-boss that had stone skin, spell immunity AND lighning enchantment. That meant no spells could harm him, all phyical attacks only did 1 point of damage (it had thousands of hit points) and every hit you DID inflict sent out spews of lighting that could kill you in one hit. A completely unbeatable enemy, and that was only an early Act 2 sub-boss. Needless to say that lead to my inactivity, since I was not allowed to advance any further in the game.
-VGsatomi