B767-300 FAILS TO MAKE XING RESTR.

Narrative

AT FL380 NEARING TOP OF DSCNT FOR XING BEARZ INTXN AT 11000 FT PRESET ON LEGS PAGE OF FMC; WE WERE GIVEN A XING RESTR OF 35 MI SE OF FWA AT FL340. I MISKEYED THE XING ON FIRST ATTEMPT IN FMC AND THEN BY THE TIME IT WAS PROPERLY ENTERED WE WERE AT THE NEW DSCNT POINT. BECAUSE OF BRAIN SLIPPAGE; AFTER WE HAD VNAV SPD AND HAD STARTED DOWN; I TRIED TO INSTALL THE 320 KT SPD REQUESTED ON THE CRUISE PAGE. THIS MESSED UP THE PROFILE AND WE WENT HIGH ON THE PROFILE WHILE THE FMC RECOMPUTED. BY THE TIME I STARTED TO CORRECT FOR THE HIGH ON PROFILE CONDITION IT WAS TOO LATE TO MAKE 35 MI SE FWA XING AT FL340. WE WERE AT APPROX FL347 AT THE XING. WE WERE CLOSE ENOUGH I THOUGHT THAT WE DID NOT NEED TO TELL ATC. ATC'S ONLY COMMENT WAS; 'WHEN YOU'RE LEVEL FL340; GO DIRECT OXI.' SUPPLEMENTAL INFO FROM ACN 693398: WHILE IN CRUISE AT FL380 WE WERE ISSUED AN ENRTE DSCNT TO CROSS 35 MI SE OF FWA AT FL340. WE STARTED THE DSCNT AND CHKED IN WITH ZID AT THE SAME TIME. THE ACFT WAS ON AUTOPLT AND DSNDING VIA THE VNAV PATH. AFTER I; AS THE PNF; VERIFIED THE ACFT WAS FOLLOWING THE PATH PROPERLY AT THE BEGINNING OF THE DSCNT; I DIVERTED MY ATTN TO OTHER AREAS OF THE COCKPIT (REQUESTING WX; CHKING LNDG WTS; ETC) AND DID NOT LOOK BACK AT THE PATH UNTIL THE ACFT WAS APCHING THE 35 MI FIX. AT THIS POINT I NOTICED THE PATH INDICATOR WAS MISSING FROM THE DISPLAY AND IT WAS OBVIOUS THAT WE WERE GOING TO MISS THE XING RESTR BY SEVERAL HUNDRED FT. WE CROSSED THE 35 MI FIX AT FL346 (600 FT HIGH). AFTER WE LEVELED I ASKED THE CAPT WHY THE AIRPLANE CAME OFF PATH(AS I WAS HEADS DOWN AND DIDN'T SEE WHAT HAPPENED) AND WAS INFORMED THAT HE CHANGED THE CRUISE ALT IN THE CRUISE PAGE TO FL340 WHICH DELETES THE VNAV PATH FOR ANY ASSIGNMENTS AT OR ABOVE THAT. I SHOULD HAVE NEVER LET MY ATTN GET DIVERTED WHILE IN THE DSCNT FOR A RESTR LIKE THAT. I WAS LULLED INTO A FALSE SENSE OF SECURITY BECAUSE THE DSCNT WAS SO SHORT (ONLY 4000 FT WHICH ON PATH TAKES ABOUT 2 MINS) AND BECAUSE THE VNAV PATH WORKED SO WELL ONCE IT STARTED THE DSCNT I FALSELY ASSUMED IT WOULD WORK AND IT WOULD NOT BE CHANGED (WHICH IT WAS). I ALSO SHOULD HAVE SEEN THE CAPT TYPING ON THE FMC BUT FOR SOME REASON EITHER DIDN'T OR IT DIDN'T REGISTER THAT HE MIGHT BE CHANGING SOMETHING WHICH WOULD AFFECT OUR XING.