So I gave the blood from the four races to Septimus, the door opened and that's as far as it would go. I had the same issues as some other reported with the quest.

I decided to walk out of the cave he's in and back in now the door is closed to even talk to him. I don't see a way of opening it, but this seems like this quest is at a stand still.

Any help would be appreciated and going back to an earlier save is not an option.

make a save before this. !!!!!

Try to kill him...

This happened to me recently and killing Septimus did solve the problem (as Mark41 mentioned). He will not turn to ash (as is intended), but at least you should be able to continue with the quest.