Why did all my rabbits die and how can i prevent this one dieing?

all my rabbits were kept outside without another rabbit and was given everything they needed but all of them died. i think it was that they were to cold but theres also the problem that i have a cat how loves to play with rabbits and a dog who won't stop scaring them. i got another rabbit today so im trying keeping her in a hutch in the garage because i bought her out of pets at home. any ideas to what i done wrong?