Hmm.... maybe I'm the one misremembering. It might've been a very late model as I remember it being relatively low-end at the time my parents bought it (they had thought computers were "buy it for life" things when they bought me the fanciest-model 286 a few years before and were real salty about obsolescence), but I'm also looking at pictures online and all the ones I can find that resemble it are, indeed, not ATX.

I don't remember the exact model, but it was a Packard Bell in a desktop (horizontal) form-factor case like one of these:

(Sources: https://vintage-packard-bell.fandom.com/wiki/3x3_v3, https://vintage-packard-bell.fandom.com/wiki/4x4_v4)

I feel like it might have been the kind with 2 5.25" drive bays, but as I said, it was relatively cheap and didn't come with an optical drive to start with so it probably should've been the smaller/cheaper one.

I was only a kid at the time; maybe I confused the reset switch for the power button.