4-year old Dell 32

Question

After the tv has been on for awhile, screen gets horizontal lines that go faster and faster and then vertical lines come on too. If you turn off the tv for about 20 minutes, it works okay. But, it starts up again after a little while. It used to happen after the tv was on for 2 hours...now it happens if tv is on for an hour. I live on Long Island. Can youhelp?