Hi, Tom,

You didn't say whether the plant in question ever bloomed originally - did
you purchase it in bloom? There is the occasional (frustrating!) orchid
that just won't flower no matter what one does.

Having said that, most Oncidiums like good light, so I don't think the
basement and low light is a good idea. Maybe some continuity, high light
and humidity, feeding normally, and less relocating of the plant will help.
Orchids like their micro climates, and they don't especially like to be
moved, unless the plant is in the wrong environment in the first place.

HTH

Diana