This phase I trial will determine the Maximum Tolerated Dose (MTD) of BKM120 when given together with fulvestrant in treating postmenopausal patients with estrogen receptor-positive (ER+) stage IV breast cancer. The toxicity profile of this combination therapy will also be described. Inhibition of PI3K by BKM120 may enhance programmed cell death (apoptosis) in estrogen receptor positive (ER+) breast cancer cells. Giving fulvestrant together with BKM 120 may enhance this apoptotic effect, providing a novel therapeutic strategy for patients with metastatic ER+ breast cancer.