Without seeing the loaves or knowing your exact procedures, it's hard to guess. My money would be on too dry a dough. Could also be inactive starter, too long a bake, not a hot enough bake, not enough rise time/temperature. So I'll just talk about how I make sourdough in the hopes it'll help. These are techniques I've learned from various books (most notably Reinhart's The Bread Baker's Apprentice) and experiences.
If I did it right, you can click any of the thumbnails for full size images.
First order of business, of course, is having a nice, active starter. I build my final starter from the barm the day before. Depending on my schedule, I either leave it at room temp all night or feed it earlier in the day and pop it in the fridge. It then comes out to warm up a few hours before I bake. It should show strong signs of life. This starter was made with nothing but flour and water--no grapes, no commercial yeast, no juice.
Then comes mixing and kneading. I like to mix the starter with the water first, allowing the starter to break up and dissolve a bit. This ensures good mixing with the final dough. Then I add the flour and salt, mix to a coarse ball...
...and switch to the dough hook for 5 minutes or so. The dough should be stickier than you think it should be. Turn it out onto a floured surface for 4-5 minutes of final kneading by hand to adjust the flour. It should be smooth and supple, still be a bit tacky, and pass the windowpane test. When you stretch it to form a boule, the outside should be smooth and not tear.
Let it rise 3-4 hours at room temp or slightly warmer (a closed oven with a bowl of hot water works well). Then shape and proof for another 3-4 hours.
I start with a very hot oven. 500-550F for artisan loaves. If using a stone, get it in there 45-60 minutes before baking, that way the stone and oven get a good heat soak. Then when the loaves go in, you want to create steam to allow the bread to rise before the crust hardens. A steam pan is a good idea, and I also spray down the walls of the oven with a squirt bottle. Be careful of squirting the light bulb--it will shatter. Don't ask me how I know. After a few squirts, turn the heat down to your final baking temp. I usually go with 450F.
Don't forget to slash them, too. That helps them expand and prevents blowouts. I had some issues getting these guys onto the stone (not my finest hour), but they were still outstanding. You can see the crumb is open and light, but still gelatinized and chewy. Perfect, in my book.
Best Answer
I think your 'troubleshooter' and the desire to know what to do to get a different result ('more chew, or a flaky crust,etc) are definitely one in the same. You'll need to understand the basic chemistry of bread (and some critical techniques as well). Baking in general is more (not all) chemistry than normal cooking. If you throw too much of something in, it may not just taste different, but change the entire critical chemical reaction in the oven.
Once that's cemented in your head, then if your bread doesn't rise, you immediately know that its one of a few things. If you want a crisp crust, you'll know what to add. Its the same knowledge.
The best two references that I've read in regards to this are :
The Bread Baker's Apprentice by Peter Reinhart - Its pretty much a classic now and a must read for anybody wanting to get into baking. Its got great chemistry, technique, and recipes in it.This is the book that made MANY things with bread just 'click' with me. A large chunk of this book deals with sourdough.
I'm Just Here for More Food by Alton Brown - Just like on TV, he goes through the why and the how of everything. It's a general baking book - not just for bread, but there's a whole section on dough. I like the techniques and understanding here, but found the recipes to be a bit lackluster. (He's got pancake info here too!)
Additionally, I'd encourage you to ask specific problems in regards to your bread issue on here. There's a wealth of knowledge on the site and absorbing some via here would be a perfectly valid resource.