FLC FMC FAILED TO INITIATE DSCNT. XING RESTR DEV RESULTED.

Narrative

WE WERE PROCEEDING NE ON J14 TOWARD THE GSO VOR. WE WERE DSNDED FROM OUR CRUISE ALT; FL370 TO FL330. THE CTR THEN INSTRUCTED US TO CROSS THE GSO VOR AT FL250. I WAS THE PF AND ALSO HAD THE ONLY OPERATING CDU. I INSTALLED THE XING ALT IN THE CDU AND EXECUTED IT. MY FO SET 25000 FT IN THE ALT WINDOW. VNAV WAS ENGAGED. AT THIS TIME THE FIRST FLT ATTENDANT ENTERED THE COCKPIT AND STARTED DISCUSSING CABIN WRITE-UPS. BOTH THE FO AND I BECAME INVOLVED IN SENDING THESE WRITE-UPS THROUGH THE ACARS AND WRITING THEM IN THE LOG. WHILE WE WERE WORKING; ZDC CAME UP ON THE RADIO AND ASKED IF WE WERE GOING TO MAKE THE FL250 XING RESTR. I LOOKED AND WE WERE 5 MI FROM GSO AND STILL AT FL330. I IMMEDIATELY CLICKED OFF THE AUTOPLT; THROTTLES TO IDLE; SPD BRAKES OUT AND STARTED DOWN. MY FO ADVISED CTR THAT WE WOULD BE UNABLE TO CROSS AT FL250. CTR GAVE US AN IMMEDIATE TURN OF 20 DEGS L AND THEN CLRED US DIRECT TO THE FLAT ROCK VOR AFTER WE HAD DSNDED THROUGH FL280. IN RETROSPECT; I MADE 3 BASIC ERRORS. 1) 1 PLT MUST FLY THE ACFT. THE LOGBOOK CAN WAIT. 2) NEVER TRUST LNAV OR VNAV TO DO WHAT YOU THINK THEY WILL. MONITOR CONSTANTLY. 3) AS YOU GET CLOSER TO YOUR DEST; EVEN ABOVE 10000 FT; THE WORKLOAD INCREASES. IT IS NO TIME TO BE WORKING ON THINGS THAT CAN WAIT UNTIL YOU'RE ON THE GND. SUPPLEMENTAL INFO FROM ACN 293436: I WATCHED THE CAPT PROGRAM THE VNAV PROFILE ON HIS CDU AND EXECUTE IT INTO THE COMPUTER AND MAKE SURE IT WAS SELECTED PROPERLY ON THE FMC. I IMMEDIATELY NOTED OUR DISTANCE FROM GSO AS THE CAPT DID ALSO AND REALIZED THAT THE AUTO DSCNT PROFILE HAD NOT; FOR SOME UNKNOWN REASON; BEGUN.