I doubt the pruning three years ago has anything to do with the lilacs not blooming now. Is there a chance you could post some pictures so we know a little more about the situation? How big were the plants before, how much were they cut back, and have they regained their previous size yet? Is fertilizer being applied (maybe even indirectly, through fertilizing the lawn)? I think something else is going on here.

I agree with brandon7 also could there be a chance that a tree has grown to shade them during this three years. Are they near a walnut or red ceder?

also .. any type of fert... might be hyper fertilizing them.. to the advantage of greenery, rather than flower ... especially high nitro fert ... like lawn fert

its not his fault.. get over it... lol

proper rejuvenation pruning requires that 1/3 of a mature plant be cut to the ground... over a 3 year period.. to insure ongoing bloom.. he just fast forwarded thru the 3 years ...

by the end of that first season after.. new buds should have been SET for year two.. unless someone else came along.. and gave it a haircut in fall ... [hopefully not him.. since i already absolved him.. lol]

ken

He actually went back and pruned them again last year, and she does not fertilize her yard. However There is an apple tree near them so it may be shading them. I will let her know. Thanks

Cutting lilacs way back all at once can delay flowering for two or three years (been there, done that). I would give them a chance and not replace them yet. Pruning should be as Ken describes, and it should be done sometime after flowering (May where I am) but before July when new buds for the next year start to set. Lilacs bloom on old wood that grew the year or two before flowering, so if they're being pruned too late in the year, the buds for next year are being removed.