Aiwa mini Hi Fi

I have an Aiwa system which has suddenly become unable to receive FM stations. It works perfectly on LW and MW but all I get on FM is very loud static. I have checked everything that I can think of and although it is not in a position where I can plug in an external aerial, I have tried it in another room where I can,but with the same result. In addition, other audios work perfectly in the offending HI FI's normal position. When I first switch on there is almost normal sound for a few seconds and then static! Any ideas, please??