Q: Transmission doesn't work when it's cold

Sounds like its almost time for a transmission rebuild. An automatic transmission has rubber seals inside similar to o-rings. These seals get hard over time and no longer do their job. Letting the car heat up also heats up the transmission fluid. This makes the rubber seals pliable again and they start working. Eventually the transmission will fail completely. The usual repair is a rebuild. There are two types of builds. A soft build that just includes seals, band, and clutches. This is done if there is no hard part damage. If it is determined that hard part damage did occur, then a hard build is necessary. This is usually more expensive because of the hard parts that need to be replaced during the build. The torque converter is also replaced during any build as it houses fluid that cannot be removed. The last thing you want is old fluid and debris in your newly build transmission. I would have this repair performed by a qualified mechanic that specializes on transmission rebuilds.