does electronic gadgets all of a sudden stop functioning when left unused

[ebo]

for say 3yrs? i moved to a small apartment so i packed my soundsystem, a desktop pc and none works now after not using them for 3yrs. the samsung lcd screen won't come on at all though the power led lights, the same for the stereo system,power light on,nothing works. they were all working perfectly before i packed them. help