how many cables have you all together mate is it 13

color H/U wire

brown = earth
brown/white = not used goes to car alarm
grey/yellow = radio illumination or dimmer wire
yellow = red wire head unit switched power
red = yellow wire head unit constant power

white/red = the rest are speaker wires
yellow/red =
white/brown =
yellow/brown =
2 X yellow/black=
2 X white/black =

the extra wire that is red should be a constant live to your head unit,
your head unit will still work with just the yellow wire connected but not properly

you could also have a short somewhere on a speaker wire knocking out the in built amp inside the H/U, but tbh you shouldn't have the red wire connected up to the speaker something sounds desperatly wrong, check your power cables first if they are all correct then i think your last option is to put your own speaker cables in