Actually, I was using Lucid Lynx Ubuntu 10.04 and by mistake mounted an empty device at /usr/src. I forgot to unmount the empty device and while I reboot Ubuntu sends me a message like this:
"Ubuntu will now start in the low-graphics mode as it can't find the configuration for relevant drivers"
And then it sits idle just like that, with a dark screen. It is providing me an option to configure the options myself. I think that this is related to /usr/src.