This is Tower Madness. It's a tower defense game where you hold off invading aliens who are after your sheep for their queen. I think she wants the wool to make a scarf.
You earn money for every alien you kill and use the money to buy weapons. I tried to create a maze out of my weapons and block off their direct route to the sheep.
But I couldn't earn money fast enough to buy more weapons and the waves of aliens overran my maze.
Those poor sheep.