Sounds to me as if the problem is in your ignition key cylinder (or rather the contacts on the back of it). Because the cylinder has to make two separate connections at the same time for ignition and for accessory, there is potential for one of them not to work. This also would explain why the radio works when the key is turned to accessory only. Most likely the contact is dirty or corroded inside the cylinder. You may be able to pull the column shroud and disassemble the cylinder to clean it. You may not be able to, in which case you would have to replace it, along with the key. Hope this helps.