I know it worked fine for some people, But after completing Diplomatic Immunity She DIDN'T give me the next quest, I'm level 50 and want to play the story line but there's nothing I can do, and I dont have any saves prior to where shes supposed to give it to you!

How on earth can you be level 50 and not have any saves prior to her giving you the quest? You actually used nothing but autosave and quick saves the entire time? If so count yourself blessed not to have gotten a corrupted save, statistically you should have lost your game by now to a CTD corruption.

No, I use Actual Saves, I'm on like my 500th save, what I'm saying, I'm lvl 50 by doing everything else in the world, NOW i chose to do the storyline, it goes smoothly until Diplomatic Immunity, where she failed to give me the quest, I just thought it was somewhere else in the game that the quest would be given to me, so i kept running around and used all my autosaves and normal saves up and i can only go as far back to AFTER shes supposed to give me A CORNERED RAT but she did not, ive talked to EVERYBODY and her no quest added.

Guessing because ive already been to sky haven temple before the quest or completed thieves guild, but idk, i just wanna play the story!

But only one slot?

Anyway, I will move this to Spoilers as this quest works, but something glitched on you, or your not finding the next step.

I use only 3 Slots plus whatever autosaves, to keep it nice and clean. I've read multiple post on different forums that Delphine does NOT give you the quest for "A cornered Rat" apparently it's suppose to start RIGHT after Diplomatic Immunity, I talked to her, Velek, Byrnjoff & Esbern! But NOTHING! I dont want to have leveled up this much and put over 280 hours into the game to NOT play the main storyline! That's what i leveled up for lol

Just make another account/character to beat the game. That's what I did. It'll only take you a few hours to get to where you are now since you should know what to do for the first quests. Some people would complain about having to play for a few more hours, but since you seem to be like me and play the game all the time you should just start over . I love fresh starts.

I might do it to get achievements

but there's no way im starting a new character after leveling mine up JUST the way i want it at level 50 lol, I put too much work to start over