I got 10 zombies... then nothing... i waited... still nothing.... Shot some trees, nothing....went away fixed a drink went to the restroom, nothing still so i shot myself after the moon had disappeared across the screen and then came back out the other saide again..
Are you upgrading your equipment then clicking continue?
The instructions say something about using an upkeep screen after each wave, but no such screen appears after I kill the first wave, nor is there anything to click on to force it up that I can find. /shrug