troubleshooting a hello world module - magento-1.7

Question

I followed a tutorial from Alan Storm on creating a basic Hello World module for Magento. After some initial problems I got it working. Today I have gone to try and expand on that and the module no longer works(I get a 404 page not found message), I have not changed any code within that module or deleted any files.
The only thing that I can think I did since first creating the module and now is go into Magento's admin screen and make some adjustments - which i've tried changing back, but I still get the 404. I also have few other basic modules that I have been working on, but they also seem to no longer work.
I have checked System > Configuration > Advanced and the modules are all still enabled
Can anyone see something in my code that would stop this module from not being found when I vist http://magentotest.local/helloworld
app/etc/modules/As_Helloworld.xml
<?xml version="1.0" encoding="UTF-8"?>
<config>
<modules>
<As_Helloworld>
<active>true</active>
<codePool>local</codePool>
</As_Helloworld>
</modules>
</config>
app/code/local/As/Helloworld/controllers/IndexController.php
class As_Helloworld_IndexController extends Mage_Core_Controller_Front_Action
{
public function indexAction() {
echo 'Hello Index!';
}
}
app/code/local/As/Helloworld/etc/config.xml
<config>
<modules>
<As_Helloworld>
<version>0.1.0</version>
</As_Helloworld>
</modules>
<frontend>
<routers>
<helloworld>
<use>standard</use>
<args>
<module>As_Helloworld</module>
<frontName>helloworld</frontName>
</args>
</helloworld>
</routers>
</frontend>
</config>
1-Would changing options in the admin area be able to stop a module working?
2-If so where do I start looking to fix the problem
3-What can I do to prevent it from happening again?