Translation:Are the windows closed? It is raining!
I am not 100%ly sure but participle forms are in Hungarian never used in a plural form - except the case, that a participle form is used as a noun.
Because of this sentence above:
"zárva" is an adverbial participle form, which needs a verb to refer on, to describe it. Without a verb it can't be used. And the verb allready takes the meaning of plural in its suffix.
Az ablakok zárva vannak. - The windows are closed.
BUT without a verb you have to use past participle form:
a zárt ablakok - the closed windows.
If I am wrong, please correct me :-)
You are generally correct, but there are exceptions, as almost always. :)
The bottom line:
- "Zárvák" used to be a valid word, a few hundred years ago. Not anymore. Do not use these words in the plural
- And these "...-va/ve" words can sometimes stand without a verb (check my second link above). But you are free to always use them with a verb.