FAILED TO COMPLY WITH CLRNC CROSSING RESTRICTION WHILE ATTEMPTING TO PROGRAM TO FMC.

Narrative

CREW LATE TO ACFT DUE TO CHANGING ACFT IN PIT AND ON OTHER SIDE OF THE TERMINAL. FILED FLT PLAN WAS DIFFERENT THAN PROGRAMMED COMPANY RMTE IN THE FMC. BOTH PLTS ENCOUNTERED DIFFICULTY IN ENTERING FILED RMTE INTO FMC PRIOR TO PUSHBACK. FINALLY GOT RMTE IN FMC DURING TAXI-OUT. AFTER AIRBORNE AND AT FL370; CTR CLEARS US DIRECT TO HANCOCK. SHORTLY AFTERWARD; CLRED US TO FL290 WHEN 40 E OF HANCOCK. LAST I KNEW; FMC WAS FLYING DIRECT TO HANCOCK AS CLRED. BOTH HEADS IN COCKPIT TRYING TO GET DSCNT INFO INTO THE FMC WHEN I LOOK UP AND SEE ACFT HAS TURNED 90 DEG R TO ABOUT 180 DEG HDG. I IMMEDIATELY SWITCH TO HDG MODE AND TURN BACK TO THE E. AT ABOUT THE SAME TIME; NEW YORK CTR CALLS AND ASKS WHERE WE ARE GOING. I SWITCH TO MANUAL ON VOR AND DIAL IN HANCOCK. I SEE WE ARE 44 MILES SE OF HANCOCK STILL AT FL370! WE ADVISE ATC THAT COMPUTER MUST HAVE HAD A 'GLITCH' IN IT. ATC REPLIES THAT THEY GET GLITCHES ALL THE TIME AND THEN ATC CLEARS US DIRECT BRADLEY AND BEGIN DSCNT TO FL290. CAPT AND I DISCUSSED WHAT HAPPENED AND WE STILL DON'T KNOW! ATC HAD NO FURTHER COMMENTS AND NO MENTION OF US NOT MAKING FL290 RESTR. FACTORS AFFECTING PROB: RUSHING TO GET ACFT OUT ON TIME. CHANGING STORED RTE TO NEW FILED RTE. TROUBLE ENTERING DSCNT INFO/XING RESTR INTO FMC. BOTH PLTS RELATIVELY NEW TO ACFT (4 MONTHS EACH). ON THE NEXT LEG. CLRNC GAVE US A NEW ROUTE FROM PVD TO DCA. AGAIN WE HAD TROUBLE ENTERING INFO. ESPECIALLY HARD TO INTERCEPT A RADIAL OFF OF A 'J' AIRWAY. I'M GOING BACK TO THE GND INSTRUCTORS AND ASK FOR MORE INFO.