This phase I trial studies the side effects and the best dose of PI3K inhibitor BKM120 when given together with cisplatin and etoposide in treating patients with advanced solid tumors or small cell lung cancer. Drugs used in chemotherapy, such as cisplatin and etoposide, work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing , or by stopping them from spreading. PI3K inhibitor BKM120 may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Giving PI3K inhibitor BKM120 with cisplatin and etoposide may kill more tumor cells.