A couple of things here.
First is that I would question if that CPU is even valid for playing the game anymore. Sure it meets the idiot specs TFP has posted, but that processor is just too old, and was only a mid-grade chipset when it was good.
Second is that you appear to have some issues with security software interfering with the game client.
(Though it is possible it is just because the CPU is overloaded) I cover this in the
Support FAQ thread.
Looks like you log in basically during bloodmoon. Player GS21, so it uses the Stage 19 horde mechanics.
It shows that it spawned about 15 zombies before you died.
Once you are dead, the horde is over until you start it again. Spawned zeds will be removed.
Looks like everything is working the way it is supposed to. If you want to re-start the horde after you have died, then you just find a zombie to hit, or restart the session. This is how it has been for a few years now.