Nandhu,
This problem maybe was from sinking much current by fan or light
This cause a ripple in your vcc
for solving this problem use an Electrolytic capacitor
for example a 1000uf between vcc,gnd
This type of caps is good for storage of charge and ripple filtering,
and:
1).Clear lcd enable pin after any use (command,data display)
2).Use stronger adaptor if fan current sinking is much
3).Check lcd pins to be sure there isn't any conductance between
2 neighbor pins

Mehdi