As MP says when you enter your password you wont see anything being entered on the screen, but it is being entered, this is a security measure so nobody can look over your shoulder… in Windows you would get a series of ****, but that would at least tell people how many letters are in your password.
So just enter your root password and hit the enter key.
If you are using Ubuntu (and you are the only user) the root password will probably be your user password.
I had deleted my previous posting, as it made more sense for you to follow MP’s instructions first… but as he’s mentioned it… here is (roughly) what it said…
What you are going to have to do is… download a LiveCD ISO image and burn it to a CD or DVD, boot from the CD and then run fsck from the command line.
Can you tell us which Linux distribution you’re using (eg. Ubuntu, Mint, Xandros, openSUSE, etc.)?.. the reason I ask is so you’ll feel more at home with the interface… in reality, pretty much any Linux LiveCD will suffice.
If you don’t have a CD/DVD drive, you still need to download the LiveCD ISO image, then use it to create a LiveUSB key, and boot from that.
Obviously you will need access to another PC and either a CD-R or a USB key (aka. pendrive, thumbdrive, memory stick, etc.)
Instructions for creating a LiveUSB key, can be found here:
http://linuxforums.org.uk/general-help-advice/help-!!!!-again/msg20412/#msg20412
The above link says you need access to a Windows PC… you can create one from a Linux PC, but I would need to know which Linux distribution was on the PC for “definitive” instructions.
If you need instructions for creating a LiveUSB key on a Linux PC or have any further questions, just let us know which Linux distribution is on the PC you are going to use for creating the key, and I’ll be happy to type up instructions. 
If you’re unsure which distribution you’re using, enter one of the following in a terminal:
cat /etc/*-release
or:
cat /proc/version
or:
cat /etc/issue
or:
lsb_release -a
or if non of the above give you anything, you could try:
uname -a
hit enter, and post back the results.
(remember - Linux commands ARE case sensitive)