flash question with the Canon D30

I have a Canon D30 camera, and I haven't yet been able to get a newer
flash for it.

I have an older Canon 300TL flash for the T90. It does work with the
camera, just not as a dedicated flash.

But I am having a problem with it. At first, it just seemed to require
a longer delay between the photos. The flash would light up as ready,
but it wouldn't fire when I pushed the shutter. If I waited a little
longer, it would work fine.

I figured I needed to change a setting or get used to the delay. So, I
started to try it again today to see if I could get an idea of how long
the delay is so that I can count and know when I can shoot again.

And now it doesn't fire when I take the shot.

It does the pre-fire flash, but not the real flash. The flash works and
charges fast.

Any ideas why the camera knows to use the preflash, but won't use it
for the actual shot? Do I have a setting wrong? On either the camera or
flash?

Thanks.