Monitor blacks out. Im having a problem with my moitor. The screen goes completely black but the

Question

Im having a problem with my moitor. The screen goes completely black but the power light it still on. It started doing this after it was used for a bit but now does so as soon as I turn it on. The thing I dont get is I took it up to best buy to have them check it out but it didnt do it there. Im assuming then that it is my computer but have no idea how to fix this. Any ideas for me? Thanks!