It most certainly is your wireless which you may need to reinstall..First a little advice.Remove what was working before as it is out of date and reinstall the drivers for your ( I assume you have broadcom wifi - most dells mini 9s do ) broadcom.
It is quite simple and here is how to do it in 4 very easy steps in your terminal.
sudo apt-get purge bcmwl-kernel-source
this removes your old driver
sudo apt-get install bcmwl-kernel-source
This will reinstall it using the best set up for your version of Ubuntu
Then the last steps areto switch it on so you do not have to reboot!
sudo modprobe -r b43 ssb wl
sudo modprobe wl
It will build the driver for you in front of your eyes.
Hope that helps