Shoutbox

try this:

right click a folder in whatever computer your accessing,
click Sharing and Security..,
then look at the bottom group and click the link that says you still want to (if its there)
then check "Share this folder on the network" and type in your share name.
Optionally if you want network users to add/delete files then press the "Allow network users to change my files".

then go to your other computer that is accessing the one you just configured; open My Documents or anything like Windows Explorer and type in the Address Bar "\\*other computer's name here*\*share name*"

like on mines it is

\\Maindesktop\Shared

accesses my folder that i am sharing.

EDIT: check your firewall and allow full access to your router (in and out)
edit2: this happened to me before lol.