single word for extensive computer user, not geek nor nerd

Power User is a good one. It signifies someone who uses the computer a lot and as such knows his or her way around quite well.

Nearly all desk jobs these days involve computers, so you can use the old fashioned term for someone with a desk job, desk jockey._{Merriam-Webster}

_{Chop Shop Store}

You can go even more old-school, and refer to a really old computer user as a keypuncher._Wiktionary

_{National Archives}

Perhaps Technophile would fit your purpose.

Noun tech·no·phile \ˈtek-nə-ˌfī(-ə)l\

: someone who likes and enjoys technology and modern machines (such as computers)

: an enthusiast of technology

http://www.merriam-webster.com/dictionary/technophile

Maybe keyboard serf. It has a nice hint at a double entendre.

Serf conveys a slavelike condition, and in particular, someone bound to the land.

1. A member of the lowest feudal class, legally bound to a landed estate and required to perform labor for the lord of that estate in exchange for a personal allotment of land.

2. An agricultural laborer under various similar systems, especially in Russia and eastern Europe in the 1700s and 1800s.

3. A person in bondage or servitude.

American Heritage Dictionary

The suggestion is that office workers are often chained to their machines. It definitely has a pejorative tone (which may or may not suit the OP). The double entendre comes from its homophonetic connection to surfing the net on ones computer.

American Heritage Dictionary

An enthusiast, computer aficionado...