No Compression

after taking all the advice from you guys I tried MMO in all the cylinders let it sit for a week.
It did not do anything to boast compression. Still zero in five cylinders and 30psi on number six. So I then tried another suggesting to pull the rocker rail to see if it was a timing issue still no change in compression. So I am still going back to my original guess that its possibly the head gasket. Is there a way to check that? I appreciate all the help in advance guys.