5 years old and 34,000 miles the car is beginning to show its age.
A guy I know has a 03 plate Yaris with 350,000 on it, another has just scrapped his 55 plate Micra with 250,000 on it as the interior was falling apart and the MOT needed loads of bushes etc and the car was worth £100.
My Fiesta is 4 year old with 113,000 on it.
Going back to your problems, like has been said, check the battery is correct. If I remember rightly from the Days I was massively into Car Stereo, the battery should be reading about 13-14 volts when the engine is running. If the power steering has any kind of hydraulic it will have a resivour somewhere, if it’s power steering on a motor the voltage could be affecting it.