I have a f250 with a 6.0 liter powerstroke desiel engine. Starting the engine when it is cold it dose not want to start and when it dose it has no power until it warms up. Ijust changed the oil and filter. Iwas startimg OK until I did that all though it did not have any power until it warmed up

If you haven't done a Tune Up in a while, would be a good time, can't hurt, if you don't have an Improvement, you eliminated a few things.
Hopefully a more useful answer will follow. A couple of talented people here.

Check glow plugs, which are used to heat the fuel:

. Testing. Use an ohm (Ω) meter to check for continuity, which will tell you if the glow plug is shot, has continuity, or is worn. Ohm out each plug through the harness. Good glow plugs will have a resistance between 0.6 and 2 Ω. If you get infinite resistance on any plug, it is either bad or the connector under the valve cover is loose.

. Removal and installation. With the engine "stone cold," disconnect batteries, remove valve cover, disconnect glow plug connector, remove glow plug with a 10 mm deep socket, install new glow plug (torque to 13 ft.-lbs.), and reattach connector. After finishing the remaining 3 glow plugs on that bank, clean valve cover, install new gasket, and reinstall valve cover (torque to 97 in.-lbs.). Do the same thing for the other bank of glow plugs and reconnect batteries. Not a difficult job--should take several hours.

Start using full synthetic heavy duty diesel engine oil--engines start easier in cold weather and turbos last MUCH longer, among other things.