I'm following through with the vampire story line, I have (had) vampire lord and the dragon summon maxed out, I'm not at the part where I'm being sent out to get the blood of a bunch of diff races. I'm not exactly sure when it happened but I went to play my game and it told me that some of the content might not be available (or something along those lines) so I pressed ok (I wasn't connected to the internet) then I fixed my connection and started playing and while I was in Solitude some guy came up to me and asked if I wanted to join the Dawnguard (which I thought was weird) so I said ok, then just continued playing well I lost my vampire lord ability and my shouts and the vampire castle isn't even on my map anymore, and when I go to the dawnguard area there's an invisible wall that's blocking me from entering and it's telling me that I can't enter. I have a few vampire skills still like servant and embrace but that's where it ends.

I dunno what to do please help!

It sounds a lot like Dawnguard was either uninstalled from your HDD or is somehow corrupted. Try deleting the Dawnguard DLC from the HDD (if it's still installed), then clearing the system cache, and then re-installing it. Also, when you are done re-insalling, go back to a previous saved game (if possible) before this problem happened or else you will likely have to start the Dawnguard questline over.

it sounds like some sort of license issue, maybe you originally downloaded the DLC on another console, or another profile? Probably just making sure you are logged in before you start the game would avoid it happening again.