One sure way of finding out if your oak tree is dead, (Assuming the
trunk is not too thick), is to scratch off some bark with a thumb
nail, near the base. If the underlying material is green or greenish
or white, it's alive. If it's brown, the tree is dead. Oak is one of
the latest trees to come into leaf in the spring, along with the Ash,
so, I agree, it may be a tad too early yet for the tree to come into
leaf. - There's a proverb, to do with whether the coming summer is
going to be wet or dry:

If the Ash comes before the Oak, we'll get a soak,
If the Oak comes before the Ash, we'll get a splash.