I'd try the feeding first, especially if they haven't been fed before. Also check that tree growth or new construction hasn't cut off the sun to the bulbs. If the leaves of the bulbs were cut off prematurely last year, that would keep them from blooming, too.
If all else fails, digging up and dividing may be the only answer, but that should be done in fall.

I agree with above. Usually I feed mine after flowering for a couple of weeks as the leaves rebuild a new bulb. I have also in the past lifted them when their leaves totally die off as I know where they are at that point. I lift divide and replant.

The only reason that I hesitate to lift the bulbs in early summer is the typical extremely hot summer where I live. If you live in an area with more moderate summers, Emilio, it should be fine to move them right after the leaves start to turn, as Sbg does.