I added two hydrangea to the gardens last year - both were rescues from the discount shelves so I don't have lots of money into them.
But both looked to be thriving in the fall of 2011. But I had an major snow storm at the end of October with out a hard frost first, an open (nearly snowless) winter and early spring snow after many things had bud break.
Both look dead - no leaf buds, but still have some flex to some of the branches.
They are in two entirely different sections of the yard - both well drained soil and enriched holes at the time of planting. One gets late afternoon sun (and that should be true all year). The other is getting full sun now, but will get afternoon shade as the trees leaf out.
So, here is is nearly May, the only other thing with out leaves is the sweet spire (clethera ) which won't break buds for a few weeks yet.
Advice please -
Cheryl southern New Hampshire. Usually a very cold yard Zone 5A with lots of wind