Question about skill activation time

First of all, i'm new to guildwars.

I was playing a necromancer recently, when I used those skills you get in the beginning (Death Swarm and Vampiric gaze) I casted Vampiric gaze first and I immediately casted death swarm after it, but the activation bar for death swarm didn't appear. Normally that activation bar shows up. Can someone explain this? Thanks.

if you press F11 and click the Interface tab make sure Skill Warmup has a tick in the box.

its possible that the weapon you have has a mod to decrease casting times of spells, which i believe causes the bar to not appear.

There's a chance you're wielding a weapon that halves casting time with a certain percentage of likelihood. It would read, "Halves Casting Time (9%)" or some other percentage. If that happens and the halved casting time is 1s or less it won't show an activation bar.