A320 CREW RETURNED TO THE DEP STATION AFTER HAVING PROBS WITH FMC DATA DISPLAY AND LNDG GEAR INDICATING PROBS. THE ENG EPR MODE WAS DEFERRED INOP PER THE MEL.

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WE WERE DISPATCHED ACFT XXXX FROM PHL-ORD WITH THE EPR MODE INOP DEFERRED AND USED THE N1 RATED MODE FOR ALL FLT OPS. WE FOLLOWED ALL PROCS; CHKLISTS; MEL INSTRUCTIONS AND DID ALL TKOF CALCULATIONS BEFORE LEAVING THE GATE. WE PROCEEDED TO TAXI WITH 1 ENG TO RWY 27L. AFTER STARTING THE OTHER ENG AND DOING OUR COCKPIT PROCS; THE MCDU FUEL PREDICT PAGE WOULD NOT ALLOW ANY UPDATED CTR OF GRAVITY/GROSS WT ENTRIES. I THOUGHT THAT IT WAS AN ANOMALY AFTER CHKING ALL WORK AND CALCULATION IN THE MCDU. WE PREPARED FOR TKOF. I (THE CAPT) WAS THE PF. DURING THE TKOF ROLL; I SET THE THRUST TO MAX N1. AS WE ACCELERATED THROUGH 80 KTS; WE WERE ALERTED BY AN AURAL AND VISUAL RETARD MESSAGE. ALL ENG AND FLT CTLS APPEARED NORMAL AND I CONTINUED THE TKOF RATHER THAN MAKE A HIGH SPD ABORTED TKOF. AFTER TKOF; I CALLED FOR THE 'LNDG GEAR UP' AND THE EMER CHIME SOUNDED WITH A RED ARROW BENEATH THE LNDG GEAR LEVER AND AN ECAM MESSAGE 'LNDG GEAR NOT DOWN.' I SILENCED THE CHIME AND WE DETERMINED THAT RETURNING TO PHL WAS THE BEST DECISION. THE ACFT WAS 4000 LBS OVER GROSS LNDG WT AND WE WENT OVER ALL ESSENTIAL INFO AND OVERWT LNDG CHKLIST BEFORE LNDG. WE LANDED WITH LESS THAN A 1000 FPM SINK RATE AND TAXIED TO THE GATE.