Ok i think I already know the answer to this one but just hoping theres a way of fixing it without spending a lot.
My wife was asked by our eldest daighter to charge her iPod touch for her, only charger we have at the moment is a portable speaker that plugs into the mains and the mains plugs into the speaker with what looks like a jack plug, my wife didnt realise the jack goes into the speakers and has managed to plug it straight into the headphone jack socket, all the ipod does now is come up with a white screen and nothing else.

post bug bump

oh dear, looks like your daughter just got herself an upgrade

I'm guessing that the speaker uses a 3.5mm jack as a charger-plug (something no devices should ever have used as it can be shorted-out whilst being plugged-in, but has been going on for decades) and that it was inserted into the iPod touch's audio socket.

Modern compact audio devices are much less resilient than older Walkman type equipment because they now rely entirely on integrated circuits, whereas older equipment would probably include a capacitor or transformer between the audio-amplifier and the output socket. Either of those intermediate components prevented DC voltage from being transferred back into the device other than as a very short pulse which would not normally be harmful (unless very excessive in size). Unfortunately those capacitors or transformers are necessarily quite large in size so they have been replaced by silicon-chip equivalents as they are much cheaper and work just as well for their intended purpose.

The downside to relying totally on silicon-circuitry for everything is if you apply many more volts than what it was designed for, then it is going to burn out pretty quickly as that voltage is continually applied to sensitive chips that aren't designed to handle anything like that the power they will be absorbing. Remote speakers probably use at least 5V, more likely 9V or 12V, and sticking that directly into an iPod touch's innards is going to fry something quite soon.

I'm afraid to say from what you've said that that iTouch is toast.