B727 WAS FOUND TO HAVE BEEN TAMPERED WITH WHILE OFF THE GATE. CIRCUIT BREAKER HAD BEEN ACTIVATED AND FO RADIO/NAV SWITCH INOP; FO COMPASS CARD HAD A HEADING CARD FLAG; HEADING INDICATING 300 DEGS VERSUS 050 DEGS. ON PUSHBACK AND ENG START; #1 ENG NORMAL; #2 ENG FLAMED OUT AND FOUND FUEL SHUTOFF SWITCH CLOSED. ELECTED TO RETURN TO THE GATE FOR A MAINT CHK OF OTHER SYS.

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UPON ARRIVING AT ACFT; FOUND FO'S COMPASS CARD HAD A HEADING CARD FLAG; AND THE HEADING INDICATED 300 DEGS. CAPT AND FO RMI; CAPT CDI AND STANDBY COMPASS SHOWED 050 DEGS. IN ADDITION; FO RADIO/NAV SWITCH WAS INOP; IE; NOTHING HAPPENED WHEN BUTTON DEPRESSED. SWITCH WAS STUCK IN NAV AND AS THE FO HAD NO OMEGA; THOUGHT IT WAS ODD THAT THE SWITCH WAS IN NAV. MAINT DETERMINED SOMEONE; WHEN THE ACFT WAS OFF THE GATE OVERNIGHT; HAD DONE A 5 STEP PROCESS TO RENDER RADIO/NAV SWITCH INOP. THEY HAD TO; IN ORDER; UNCOLLAR A CIRCUIT BREAKER; PUSH IN THE CIRCUIT BREAKER; PUSH FO RADIO/NAV SWITCH TO NAV; PULL OUT THE CIRCUIT BREAKER; AND COLLAR IT. MAINT FINALLY CORRECTED THE PROB AND WE DEPARTED AT XA09Z. AFTER PUSHBACK; THE #1 ENG STARTED NORMALLY; HOWEVER #2 FLAMED OUT AFTER START. THE ENGINEER THEN FOUND THE #2 ENG FUEL SHUT OFF VALVE WAS CLOSED. BECAUSE THIS WAS THE SECOND EVENT THAT TOOK HUMAN INTERVENTION TO CAUSE; ON THIS ACFT; I DETERMINED THE SAFEST ACTION WAS TO BRING THE ACFT BACK TO THE GATE AND HAVE MAINT DOUBLE CHK SOME AREAS THAT SOMEONE MIGHT HAVE ALSO FOOLED WITH. IF SOME UNKNOWN PERSON OR PERSONS HAD NOT PERFORMED 2 UNUSUAL ACTS ON THE ACFT; WE WOULD HAVE DEPARTED AND ARRIVED NORMALLY.