ok so i downloaded dawnguard , i know ive downloaded it properly because when i click start a icon box appears and says " loading downloadable content ".
and ive been trying to talk to guards in major cities but there not mentioning anything about vampires ,
so i dont know where to start .

can someone give me a direction to head towards so i can start my new DLC ?

I've heard restarting fixes this. If your not level 10 you won't hear rumors though.

im lvl 53 lol

Go to riften and an orc will approach you.

Try restarting Skyrim then. I heard people say it fixes it.

Can be any major town.

I got the quest from a guard in whiterun when I walked past him about 15-30 minutes into playing. I didn't even have to initiate conversation. He just started talking about it.