How do you fix a t.v. that keeps turning off?

It depends on what type of television you have. The different types have common symptoms and without knowing if it's a CRT analog set, DLP, LCD or projection set, it's too difficult to even venture a guess. What is happening most likely, is that the television's microprocessor is sensing something wrong in one of the areas of the set and it's going into a self-protect shutdown mode to prevent any further damage. If you're not electronically trained, I'd suggest you call a service technician out, but plan to spend some major bucks. I just hope you have an extended warranty.