Toshiba windows won't load

Hello, I have a toshiba and when i turn it on it shows the title "Toshiba" on the screen but after that it shows the screen mircrosoft corporation with a loading box of course but the screen stays there with the loading box forever it doesnt want to change the screen. My sister left the computer on for a day with the screen saying microsoft corporation but it doesnt change the screen. WHAT CAN I DO PLEASE HELP!!!!