Vista - Black Screen Blinking Cursor

OS is Windows Vista (had SP2 and latest updates), Inspiron 1720. One day, walked up to the laptop and it had a black screen and blinking cursor.

I power down and on dozens and dozens of times since then - happened a few days ago (07-17-2012) . Each time I power on I see the initial F2 & F12 Dell screen, then goes straight to black screen with blinking cursor. F8 has no affect and never get anywhere near to Windows Vista booting. Tried Vista restore from Dell disk several times and doesn't work and doesn't detect any problems. Ran all extended hardware and memory diagnostics that came with the Dell computer and everything passes. Tried new Vista install, which then requires a reboot to complete, then went right back to black screen with blinking cursor.

Been scanning and scanning the internet... have hit a major logic gridlock as to what the problem could be. All hardware appears fine and passes all tests. Then tried new Vista installation and still get the black screen with blinking cursor. I am very desperate to get this fixed. My wife needs this up and running for work come early Monday morning.