This phase II trial is studying how triapine and cisplatin given together with radiation therapy works in treating patients with cervical cancer or vaginal cancer. Triapine may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Drugs used in chemotherapy, such as cisplatin, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Radiation therapy uses high-energy x-rays to kill tumor cells. Giving triapine together with cisplatin may make tumor cells more sensitive to radiation therapy.