HELP!

I finally got the Tartine baking book and no matter I can't seem to get started right.  I've followed the instructions for the starter to the T and everytime it seems to be going fine.  Lots of bubbles, bit of a stink - everything looking good.  But then I feed it and inevitably the next day it appears all seperated and funky.  There's been a layer of yellowish water on top and very little bubble and no matter the consistency when I start it turns out very thin and runny.  I've never had a crust form but the last batch even had fruit flies swarming towards it.  

Since it always seems to so south after about the fourth or fifth day I have restarted from the beginning three times now and just don't know what to do.  Could it be that it's too hot in my kitchen?  We don't have AC and its typically in the low 80s minimum in the kitchen.  Is my flour rubbish?  Am I just a terrible baker?

Any suggestions would be greatly appreciated - I was so excited when I found this gorgeous book and thought I would finally have an in to switching to all homemade bread.