Within Temptation

which one of them is power metal?

There's no pure power metal here, and I don't really like it, but Symphonic and with a touch of Gothic – that's After Forever.

Isn't this modern metal, or are they already playing gothic?

Melodic Metal and Modern Metal, they're not related to Gothic.
The genres I mentioned in the previous message are too strict; each band has a different approach – their albums sound different in different years, so please don't judge too harshly.
I just wanted to say that you shouldn't focus on just 2-3 bands; you need to broaden your horizons – I myself used to only listen to WT and LC, but I'm still looking for interesting bands in similar genres and styles.