changed steering column, won't start

Most likely your anti-theft is activated - do you see a flashing light?. The anti-theft system in a 99 Taurus is the PATS (passive anti-theft system). The column ignition switch has a antenna ring around it to interact with the transponder chip in the key, if the new column did not have that ring or it's not connected properly, key cannot be read and no start. You might be able to transfer over the old ignition switch to resolve this problem. FYI (if I recall correctly) the PATS in a 99 Taurus is not in a single module but integrated into the PCM/HEC and several other modules, depending on exact flavor of the system used on yours. For now, try and determine if your no-start is caused by the PATS.

the problem is with the ignition switch- not the column- like ken says, there are electronic problems- you may have to get an new ignition switch and key- maybe even have a dealer do this- i know it is expensive, but that's the way cars are these days-