My main character is a sorcerer. My party includes Yoshimo, Minsc, Jaheria, Aerie, and the Paladin(whatever his name is). Anyway, I went to the Pirate Lord, but didn't like how Yoshimo seemed to be able convince him just by dropping his name to let us into Spellhold. Instead I went to the Cowled Wizard, killed him and got the stone and book. I made it past the defenses of Spellhold, but when I opened the front door my stone disappeared.
My real problem is that when I go into Spellhold, all the doors are magically locked and there is nowhere for me to go. I can't get outbecause Spellhold's defenses now keep me in. Unfortunately, I foolishly utilized the quicksave to the point where my last save is back at the end of Chapter 3. Do I just have to go back there and do it again, or am I missing something?

I am not sure about this as I've only used the Pirate Lord option (and killed the Wizard anyway heh) but I think you're still doing fine
MAJOR SPOILER AHEAD
>
>
>
>
>
>
>
I think in some time Jon Irenicus will appear and take you prisoner. Just wait till that happens (maybe rest a couple of times.) I still think the other option of gaining entrance to Spellhold is better, since you get to meet the other prisoners. I'm not sure if that will happen if you got there on your own.

I rested 8 times...do you think this is a patchable thing?

I'm not sure...I don't know if I might have missed anything else: like I said I didn't follow the same path as you.
I see only one solution: someone else please help Virgilxx out!!!!!!!!!!!!!!!!

are you a paladin? If so that explains it. The patch fixes it.

The patch fixes it also did you get the stronghold? If you're desperate use shadowkeeper to recreate the stone and use the other way. Also make minsc talk to the pirate it is one of his best lines in the game. example,
Minsc:Where's your peg?
Pirate: What?
Minsc: Your peg all pirates have pegs.
Pirate:?
Minsc: And where is your pariot? All Pirates have a peg and a pariot. Just like all Rangers have hamster!