Master Boot Record.
First thought, restart in Safe Mode and choose Last known good configuration.
Second thought, restart with the XP CD and choose Repair. If you can get to the DOS-like repair screen, type:
Press Enter. Accept.
My Dell Inspiron 530 worked fine yesterday. Today when I turn the power on I get the Dell screen with the f2/f12 options followed by a message that windows did not shut down properly with options for safe mode or normal mode. I have tried both options and after the screen shows the microsoft logo with a status bar briefly the screen goes blank and nothing happens. The machine is running Vista Home Basic