I think my starter died

I'd try adding more water and flour.  If you go with a recipe such as Peter Reinhart's Mother Starter refresher (p. 42 of Artisan Breads Every Day) ... he calls for 2 3/4 cups of flour and 1 cup + 2 tablespoons of water per 3/4 cup of starter.  Since you have 1 cup you could up the flour a bit - I'd try adding some more flour and water and see what happens.  Let it sit at room temp for 4-8 hours and you should get some activity.

Try that and let us know what happens.

-Trevor James

A half a cup of flour to feed a full cup of starter is woefully insufficient.  I don't know what hydration you are keeping it, but it needs to be fed more flour.

You probably want to use more flour and water.  When I feed my starter I always use at least 1:1:1 starter:flour:water ratio.  If I want a lower hydration level starter I use less water but at least the equal amount of flour to starter.  If, increasing amount of flour & water doesn't  seem to help you may want to try force feeding it for a couple of days.

My starter did something similar to me once.  For no particular reasons it seemed to die on me while I house sat for my friend.  My husband didn't know how to feed the starter so I brought it with me.  Good thing I did or I would accuse my husband of killing it LOL Anyways, I ended up force feeding the starter (fed it 2 - 3 times a day) and put 3 - 4 raisins into the starter and let it do its thing.  After 36 hours, my starter became bubbbly and smelled like starter again.   Hope yours will do the same.

Best of luck!

Al