Absolute newbie to Linux - unable to enter password.

Ubuntu Linux ver 9.10.  Have been trying to fly with Ubuntu for a couple of weeks, installed without problems, bought the book, downloaded the command cheat sheets, experimented offline - no major hassles. 

I now have a problem with the user password when trying to use the sudo command (and it has been working).  I've done something which stops the user password being entered, the password bullets do not appear on-screen and a blank password is not accepted.  I appreciate that a re-install will probably fix this but don't want to get into the habit of re-installing to fix what could be simple to rectify.  Re-booting does not fix the problem.  Any ideas appreciated.

Based on my limited experience with Ubuntu (running 9.10 under dual-boot with Win 7), the only thing I can suggest is what you'd rather not hear, which is to reinstall Ubuntu.  However, in case you're not aware of it, I'll suggest you post on http://ubuntuforums.org/ since it's a forum focused on Ubuntu. 

If you find a solution without reinstalling, I hope you post the solution here so we can all know it.

Thank you Soybean.  Turns out that what I was viewing on the screen is normal for Ubuntu Linux but my interpretation of it was incorrect due to my lack of knowledge.

I took your advice and signed up at UbuntuForums, the thread can be viewed here.

Glad to hear problem solved, and thanks for posting your findings on that.