Welcome to Orchid Board. It really depends which type of orchid you are referring to, but I am assuming you mean Phals.
Posting some pictures of them would help. Phals do not require a lot of light, so that is not likely a problem. Any hot or chilly drafts on new buds could cause them to blast. Also leaving fruit such as bananas in the vicinity can cause blasting due to ethylene gas released by ripening fruit.
I find my Phals like a cool drop in temp for 4 to 6 weeks in the fall and this will initiate a bloom spike. But if yours are on windowsills then come fall, they likely get that drop. If the temps are above 15C they should be OK.
How are the roots? If it has poor roots, it may not be able to support blooms.
These are a few things to consider.