First check the canes on the dead roses. Are they chew marks of beetle tracks? Second look at the roots, Are they brittle? Easily breaking? Or, Long and Nimble?
Now, if the crew marks are beetle tracks you will see signs of chewed up rose stem inside the stem itself, then its infestation. If is is actually chew marks then its a hungry animal out for a quick meal.
If the roots are brittle and easily break, the rose froze to death. If they are nimble and bend easily without breakage, then the hungry animal(s) got your rose.
Consider planting a newer rose where the old ones sat, but lone the hold with burlap then plant your rose, that will stop the cold from harming the root system. Consider, this winter placing a small fense around your roses to prevent hungry animals from a quick meal. Then condider using vegetable oil (won't harm the rose) on the stems just before your winter sets in, this will prevent insects from nesting there during the winter months. -Birdy