Password Problem after downloading and installing 185 updates to UBUNTU 8.04 and associated software.

I have only had my DELL Inspiron Mini 9 for 2 weeks. I am new to UBUNTU and I am not a techie! On 23 April while I was online via a wireless connection the system told me there were 185 updates to download and install. I followed the on screen instructions and seemed to succesfully download and install the changes. I noticed the difference after upgrades particularly that it was easier to get on to wireless networks andsome of the symbols on top right of screen were different e.g. state of battery charge. I continued to use the machine successfully on several wireless networks but when I returned home on Sunday 26th April and tried to set up a connection to my wired network there I found that my password I need to access administration tasks was no longer accepted and I had not changed the password!! How do I get out of this? Help!!!