Well my settings are pretty default too. I did change some small things in the httpd.conf to get stuff like php working. But nothing special I can think of.
I also have a portable web server on one of my USB sticks. At the time it didn't work on my local webserver, the same problem occured on the portable web server. But when when it suddenly started working again on the local webserver, it also started working on my portable webserver. The portable webserver I used is called USB Webserver 6 which has the same versions of apache and php as my local server. The USB version is preconfigured, so there isn't much I changed there. So I doubt that it has something to do with the configuration.