Windows 7 Toshiba Satellite L505

Hello,

I have a windows 7 Toshiba satellite L505 and the problem is that the laptop won't start up! I shut down the laptop and charged it for a bit. When I hit the power up button the laptop screen shows the Toshiba logo and then a black screen with a white underscore at the very top left corner, about 3 seconds later the screen shuts down on its own and starts the process again. when it shows me the Toshiba leading innovation logo it does give me the options of f2=setup utility and f12= boot manager. Before any of this begin to happen my laptop started to act up and run really slow. Someone please help!