Mac - Windows File Sharing not working

Hi there,

I want to use Lion's SMB File Sharing from my MacBook Pro (mid-2012) and my PC running Windows XP. Currently, my list of Windows users on my Mac is empty, and everytime I try to log in from my PC, I get a prompt asking me to log in, but no matter which passwords I enter, they don't work.

Can anyon help me? Thanks!

PS A bit off topic, but my Screen Sharing option is missing too...