We cannot determine exactly what the problem is from the photos. It would be helpful if you sent us a wide-angle photo in a reply. These do not show insect or disease problems.
Lilacs need a cold winter to bloom, otherwise they have few blooms and the blooms they have are small.
Lilacs like a higher pH (not acid) soil--pH about 6.5 or 7. You can have the soil tested to determine the pH and see if the soil needs lime to raise it to better pH.
The third photo of the branch looks like mechanical damage. However, Europen hornets often strip bark off lilacs and this can kill stems. Click here for more: http://extension.umd.edu/hgic/european-hornets
Your lilac also may need pruning to rejuvenate it, depending upon its age.