Does not sound good for your Japanese Maple. By now, it should show some evidence of growth. Are the twigs pliable or do they snap if you bend it? Scratch away the bark to see if it's green or brown underneath. If it's brown, it's dead.

Hi Rhiann and welcome to GoY. I would certainly have expected to see leaf growth by now but one of ours is just, and barely coming into leaf - this is always a late one though. As Bathgate suggests gently scrape away a little of the bark with your fingernail if there is green underneath it is alive brown and it is a goner... They can suddenly turn their toes up for no apparent reason.