1520 Dell Inspiron startup

When I turn on the laptop, the laptop is very, very slow and able to load initially, when the screen shows the Dell logo. The screen shows its trying to go to the next step of opening my Windows Vista but just provides a black screen and just a flashing cusor. Thats as far as it will load. I have shut down and restarted the laptop but same thing. I have hit the F2 key and finally after the fifth try it started in the setup mode and I hit the escape key . It then finally started up and then everything seems to work just fine. It is only when i shut the laptop down i have this problem. Can anyone help or give me some type of direction on which way to go. I am at the point I will not shut it down anymore being afraid I can never get it started again. Am I missing some bios? Is the laptop hardware broke/missing some files? Please help with some type of actions you may want me to try. Thanks for your time in advance, 12gage