Hydrangeas like soil that has a balanced ph level. There are commercial potting soil mixes for these type/family of plants, "hollytone" is one good brand. The ph level also determines the color of the flower, which can change due to the ph. As to the browning of the foliage, possible causes are, it was heat damaged and cannot now be brought back by watering; or it has powdery mildew disease which requires a chemical treatment. A good resource for plant diagnostics is your local cornell univ. Cooperative extension, if available. Also, ask at the nursery or plant store where you bought the plant. Sometimes plants are sold that have diseases and you don't see this until some time after you've had the plant. What a shame! Get yourself a new healthy plant and enjoy!

 Re-mix soil with one part regular old backyard dirt, only water a little bit and by that I mean count to 5 plants stay alive.

 They need more water sunlight and other stuff

 I suggest that you water it more and keep mild sunlight to it...this should help it.

 I say water it and put it in the sun make sure no bugs (beatles,sslugs) are on it!!!!