First, neither forum you selected is appropriate for your question. This is a plant care question and has nothing to do with design. Would have been better to post in the Hydrangea forum. The more suited the specific forum you post to, the better the responses will be!

We can start by establishing that hydrangeas make very poor houseplants, as does any plant that can be easily grown outdoors. Indoor conditions are just not at all to their liking - wrong temperatures, too low humidity, inadequate sunlight, etc. They will invariably struggle to survive. Florist's hydrangeas - small plants forced into bloom out of season and sold in grocery stores, etc. - are intended to be temporary indoor decorations.....little more than cut flowers :-) Enjoy them while in bloom then toss as they decline.

In some cases, they can be successfully transitioned to outdoors. But that assumes you live in a climate that is conducive to their growth and that you can keep them healthy and alive until it is safe to plant.

Without a photo to visually illustrate what is going on with your plant, it's hard to know what's happening. It could be that the current flowers are just going over and drying/turning brown. If it is more than just the flowers, then chances are very good it is something to do with water - keeping the plant too wet or allowing it to dry out. What it is planted in will also have a bearing on this.

To care for a hydrangea indoors (and only on a very temporary basis), it needs to be removed immediately from any plastic or foil wrappings. Make sure the pot it is in has an adequate drain hole. It needs a cool location with lots of bright light but no direct sunlight. The soil it is in needs to be kept just moist to the touch - not too wet and not too dry.

If your plant survives and you live in a climate where it will grow happily outside, you can gradually transition it to the outdoors when temperatures warm up. And my concern here is that if you were in a such a location, you could already begin this process - where these hydrangeas grow best, it is already warm enough for it to be outdoors.