[verb (plain)] + はずがない [i-adj] + はずがない [na-adj] + な + はずがない [noun] + の + はずがない
はずがない means "there's no way that…", "it can't be that…": going by what the speaker knows, the thing cannot be true. It follows the plain form, present or past; a な-adjective keeps な and a noun takes の.
はずがない denies the whole idea. A negative verb before はずだ is milder: it says what you expect, and you could be wrong.
These go beyond plain はずがない.
In polite speech the ない becomes ありません.
With は in place of が the denial is a little more pointed. In casual speech the particle drops out altogether.