Hi CHIKO, now I am more confused after your last post. could you state your vendor for more specific investigation.
Try if the hardware is ok, try setting BCCH on that TRX. obvoiusly thats not possible if that TRX is DCS of concentric then try lineanting you Zone Thresholds and locking other TRXs of DCS that way the assign failures might increase but the TRX should get traffic. By the way do you have assign failures on that cell or not and if possible try the Abis traces.
But do give more information. like vendor TRX Zone, Z0ne thresholds, what happens when other TRXs are locked etc.