TV has audio sound and no picture. hello,i have the TV trinitron 36XBR400 about 6 yrs old. when

Question

hello,i have the TV trinitron 36XBR400 about 6 yrs old. when i turn TV on, i hear sound only with no picture (black on screen). i turn it off. it goes off and i haven't seen any problems. i turn it on again. i hear sound without pictures. Do you have any ideals what cause problem? How do you fix it?Thanks,trungno picture only sound