Got stuck in Chaos Sanctuary, now what do I do?
This is the N-th time I've tried to beat Diablo 2, and it's happening all over again.
I'm a Paladin at lvl 28, ripped through the game without much difficulty until Chaos Sanctuary. As soon as I release the 5th seal there, a bunch of lightning-fast Venom Lords spawn and kill me with one-two hits (an my merc along with me). I opened a portal beforehand so I just grabbed a few spare items from my chest and when I returned to just loot my corpse real quick, portal back and re-supply, I was killed again - in one hit.
Now, why does this happen and what am I supposed to do now (portal gone, butt-naked and no decent stuff in pandemonium fortress' shops)?
The short answer is you were too low level / not geared up enough for the Chaos Sanctuary.
As pixel noted in the comment, you can leave your game and re-enter to have your most recent (or highest valued) corpse returned to you in town. It's best not to wait until you have a lot of corpses, if you need to do it, just do it.
Nextly, you need to go back and run act 3/4 again and find some better gear before attempting the Sanctuary. It's quite common in the Diablo franchise that you don't find the gear you need until after it's useless to you but it's a cross we have to bear. A few levels will help.
Beyond that you'd have to expand your question with your current skill tree, gear and stats for us to give you much more specific advice.