TV Black-out

Question

My TV screen goes blank but the sound stays on. The screen is on at first but reduces to a white center dot and goes black but the sound stays on. When it is turned off and put back on, the screen comes back to life. This may happen a few times and then it stays on for the rest of the evening. The frequency of the blackout has increased from once in a while to a few times a viewing. Sometimes it is okay. A tap on the side seems to work sometimes. What is the problem and is it fixable and worth it? Can I get a part and replace it myself? It's been a great TV. ThanksFranko