B757-200 FLT CREW ON RIIVR STAR TO LAX REPORTS CHANGE IN RWY ASSIGNMENT AND INAPPROPRIATE ALT AND AIRSPEED CLRNCS FROM APCH CTL CAUSE THEM TO BE TOO HIGH AND TOO FAST TO MAKE A TIMELY DESCENT AND LNDG.

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THE FLT WAS CONDUCTED WITHOUT INCIDENT UNTIL APCHING GRAMM ON RIIVR 1 ARR INTO ZLA. AS THIS ARR IS USUALLY ASSIGNED RWY 25L FOR LNDG; WE BRIEFED THE RIIVR 1 ARR TO LNDG AT ILS 25L. THE ACFT WAS CLRED TO DSND TO FL270 AND THEN SUBSEQUENTLY TO FL240 BY GRAMM. WE COMPLIED AND MET THE ALT RESTR. UPON CHKING INTO SOCAL APCH; WE WERE ASSIGNED RWY 24R AS THE LNDG RWY. WE WERE THEN CLRED TO DSND TO 14000 FT BY RIIVR. AS PF; I MANIPULATED THE AUTOFLT SYS TO MEET THE NEW RESTR WHILE THE CAPT AS PNF REPROGRAMMED THE FMS TO ASSIGNED RWY 24R AS THE LNDG RWY. DURING THE DSCNT WE WERE DIRECTED TO MAINTAIN 300 KIAS. I MANEUVERED THE ACFT TO COMPLY WITH THIS INSTRUCTION. AFTER LEVELING OFF AT 14000 FT AND NEARING RIIVR; WE QUERIED SOCAL FOR LOWER ALT. WE WERE INSTRUCTED TO MAINTAIN 14000 FT AND INCREASE SPD TO 310 KIAS. WE COMPLIED AS DIRECTED. PAST RIIVR WE WERE INSTRUCTED TO PROCEED DIRECT SKOLL AND TO DSND AND MAINTAIN 10000 FT. WE WERE NOT IN POS TO MEET THE 250 KIAS AT 10000 FT RESTR BY SKOLL. WHILE THE PNF WAS SEQUENCING THE FMS TO PROCEED DIRECT TO SKOLL; THE COPLT'S CDU WENT BLANK AND COPLT'S NAV DISPLAY LOST THE MAP DISPLAY. THE COPLT'S CDU DISPLAY RETURNED WITH FMS RE-SYNC MESSAGE. I SELECTED HDG SELECT TO MANEUVER THE ACFT TO INTERCEPT THE RWY 24R EXTENDED CTRLINE. AT THIS TIME; THE CAPT RPTED TO SOCAL THAT WE WOULD BE UNABLE TO MEET THE 10000 FT AT SKOLL RESTR. RATHER THAN ADDRESSING THIS RPT; THE CTLR THEN ISSUED A HDOF TO THE NEXT SOCAL FREQ. WHEN THE COPLT'S FMS RETURNED ONLINE WE WERE 1.6 NM FROM SKOLL AND DSNDING THROUGH APPROX 12000 FT. UPON CHKING IN TO THE NEW CTLR AND APCHING BREEA WE WERE ASSIGNED 310 DEG HDG TO LOSE EXCESSIVE ALT. UPON REACHING MORE REASONABLE ALT; WE WERE ISSUED CLRNC FOR A VISUAL APCH TO RWY 24R. SUBSEQUENT VISUAL APCH AND LNDG WAS COMPLETED WITHOUT INCIDENT. THE TEMPORARY FAILURE OF THE COPLT'S FMS ADDED TO THE WORKLOAD IN THE COCKPIT. BUT THE REAL PROB WAS THE INSTRUCTION TO MAINTAIN 310 KIAS AT 14000 FT WELL PAST THE POINT FROM WHICH A SAFE AND ORDERLY DSCNT TO A NORMAL APCH PROFILE COULD BE MAINTAINED.