dead live rock

when my tank crashed about six months ago I took the live rock and put it in
a dry plastic
barrel.

ok so now its dead rock. yes I know I can reseed it with some new live rock
and I can buy a bottle of cycle bacteria in a bottle?

the question is if I just fill the tank with salt water and put the sand -
rock in will any
bacteria grow if every thing has been dry for months or is it a MUST to add
some new live rock to start the process.
how would you go about restarting this tank. I am going to be buying
some more sand
to make the DSB deeper than it was.
Im sure my LFS will give me a cup of live sand to seed mine they are good
like that.

David