Why do my fluorescent lights turn on slowly or not at all in the summer?
Almost certainly the ballast, unless old enough to actually have a separate starter, at which point it becomes a tossup between ballast and starter - probably not from 1992. But a 1992 ballast is certainly ripe for replacement 22 years later. They don't live forever.

I have a few older ones I have not gotten around to replacing that are very humidity-sensitive (a little bit heat, a lot humidity...at least in my case.)