how can i fix my television?

My television will turn on, but it will not stay on unless we keep clicking the channel button over and over again, once the "sound" goes away then we can get the tv to stay on and the picture and everything is fine. Here lately though it seems like it is taking a longer and longer time to come on. What can we do to fix this problem? This is a 27" Phillips television Model number 27PT543S37A