Have the world keep using CRT (Cathode Ray Tube) televisions rather than switching to newer television models such as LCD or plasma.
That is tough to do. Flat screens and hd tv are big improvements over CRTs. And unlike HD-DVD vs. Blu-Ray or VHS vs. Betamax, it isn't just a format issue with slight differences in quality or features. I think you have three tools that could each slow down flat screen adoption. One is technical mistakes. Get people working on solving the wrong problems or hung up on a technical mistake that takes them down the wrong road. Maybe something like flexible screen technology seems like it is right around the corner and diverts research. Another option is regulation. Protectionist laws pushed by suppliers of older technology might create unreasonable technical specifications, requiring inefficiently high resolution, unattainable levels of energy efficiency or redundant and expensive safety features in addition to attempting a straight up ban. Also, a company sitting on a necessary technology's patent, either trying to work out their own system or trying to extort producers for outrageous sums could leave research stalled or slowed trying to find a work around. The last is disastrous PR. An initial launch that is unreliable, poor quality, or undersupported (perhaps with very little HD programming being available, for example) could slow adoption. Also if companies use a lot of proprietary devices, so you have to have a special kind of DVD player or power adapters or cable boxes in addition to the cost of the TV.
You might also have a new generation of CRT TV with distinctly better features than our last generation of high end CRTs come out just before the launch of any potentially really successful competing technology. That both extend the CRTs at least one more cycle, and makes flat screens look that much more unprofitable, or at least denies a bit more funding to the would be manufacturers.
But at best I think you are slowing the end of the CRT. It may last long enough that it isn't our modern type of flat screen that replaces it, but some other tech, but eventually, the downsides in terms of picture quality, space taken and power consumptionare going to make them outmoded.