AM 1808 system Mallfunction

hi, 

I am working on AM 1808 system, some times system is suddenly malfunctioning as 

     1) LCD goes off and only shows Blue screen, but the vsync,disp,DE to LCD are working fine

     2) At that time, all the voltage levels and clocks to ram and processor are fine

     3) But the data lines to RAM are freezed, the RAM we are using is MT46H32M16LFBF

     4) No data appears on the UART even to communicate with the system.

Please give me any suggestions regarding this issue.

Thank you,

Sreenivas