My Kia Ceed is a very similar vehicle to the i30 and shares a lot of components. Mine is an 08 model which I bought recently and appears to have spent the last 10 yrs in a basement parking garage dry, warm, and dust free. It looks like a showroom new car, Clocking up just 10000 km during the last 10 yrs. However the radio / stereo seems to have a similar issue, the cause is the on off switch. A fix could be to wire in a separate on/off switch on the main power supply or yellow wire if it has one and use the new switch instead of the main one. To get the stereo to work I guess one would have to get access to it and either fix or replace the main switch or put it into a permanently on condition. Try holding the switch in for a few seconds, disconnect the power for a "reset" and that kind of thing it may come to life. Currently I just don't turn mine off.