I started the quest "Joining the Stormcloacks" and never finished the quest and continued to do the main quest. Eventually when i got to the point in the main quest where you must get the imperials and the Stormcloacks to make peace, Ulfric will not talk to you and tells you to finish the "joining the StormCloak" quest and even if you do finish that quest, he still will not talk to you and you cannot continue doing the stormcloack quest or the main quest, making the main quest impossible to finish unless you restart. What to do?

I believe you need to get the jagged crown before he talks to you.

You can't. If you talk to Ulfric, he tells you to speak to Galmar. When you talk to Galmar, he goes off about you convincing Ulfric to the peace treaty. You can't start the Jagged Crown quest and you can't continue with the main quest.

Join the imperial army if it's impossible, that's a possibility? you can still choose the imperial army i believe as long as your not a full member of the stormcloaks?