Lilac bush won't bloom
Thank you for your question. Without actually seeing your lilac bush and only going by what you said, I believe the problem is caused by bacterial blight. I have included a link below to an article on the disease. Read it over, look at the pictures, and see if this is what the problem is. The article also explains what can be done to help your plant. If you don't think it is the blight, then let me know. A picture of the affected blossom and surrounding stem may help me figure out what it is.