Question: Reviving a Sourdough starter
By: Rich Grant
Published: August 3, 2010

My sourdough starter seems to be losing it's zip. Anyone have any tricks to getting some life back into it?  It's not dead yet, just not very lively.

Thanks Much!

Answers:
Chris Paulk

Discard 1/2 the starter and then feed another 1/4 cup water and 3/8 cup flour every 12 hours or so. When the starter is doubling between feedings, feed it one more time, clean out the storage jar, put the revived starter into the jar, and put the jar back into the fridge. 
From Sourdoughhome.com
He has a good blog (though no pictures) about baking and some good tips.
Barnaby Dorfman

Try adding small amounts of sugar and also allow it to warm up to room temperature over a several hour period. Look for bubbling as signs of life.