TOTAL noob here, having installed Ubuntu 14.04 on my laptop (with some difficulty, as I have no clue what I'm doing).
I set a strong login password that continues to let me log in to my system. I can access the preinstalled apps, surf the web, etc. However, the Software Center refuses to accept my password and indicates it cannot authenticate because I require privileges (mine is the admin account). I dug around a bit and tried the passwd command to change passwords -- system told me there was a manipulation error and wouldn't recognize the password I'd just used to log in. Tried a different command, and got the same result. Oh...I also checked for the obvious, like the right keyboard layout etc.
I'd love to install some additional software, but other than play around with what's currently on board, I can't do anything. Any help or suggestions greatly appreciated. To make matters worse, I'm not merely a noob; I'm also an old geezer, and not as quick on my mental feet as I used to be...:)