Kessex hills
If you are too low level for monsters, you deal glancing hits. If you attack a monster and it’s invulnerable, it probably mean’s the monster can’t get to you, so the anti-cheat system makes the mob immortal, so you can’t afk-kill
You are a bit under-leveled for Kessex Hills, or at least the area you have entered in Kessex Hills. You can level up more in other starter areas, if you so desire, or by mapping the 6 cities.
Here is some information about being under-leveled against foes: http://wiki.guildwars2.com/wiki/Level#Exploring_high_level_areas
Good luck.
Thanks guys,
I hadn’t realised I was going too quick. Will go work out a bit!
Jon