How works ReInstall OS X Lion on Macbook

I got a new hard drive cause my old one broke, anyways iam connexted to the internet and i already bought the os x lion with my apple id.

it always says the product is not available at the moment.

i cant even use the apple support cause i dont know my serial number.

does someone know what i can do to get the macbook fixed?

is it okai if i just go inside an apple store and they will help me for free?

thanks in advance!