Everyone seems to be having fucking trouble with this shit, so here's how to make it work...
What YOU have to do
1.
Register to get your own username and profile.
2.
Download a plugin for your music player, and enter your login details.
3. Listen to some tunes
^^Simple enough?
It should ask you to sign in after you download and INSTALL the plug-in, not just download. IF it doesn't ask you to sign in with your Audioscrobbler name and password, then do the following (assuming it's for Windows Media Player):
open windows media
make sure its in the mode with the tabs
in the top right corner will be a little upside-down triangle
click it, go to Tools, then Plug-ins
Make sure that the Audioscrobbler has a check next to it
Then open the menu again, go to Options
Click on the "Plug-ins" tab and then "Background"
Right-click Audioscrobbler, go to properties and SIGN THE FUCK IN
If it still doesn't work for you, you are prolly just gay.