Hi Cia,
It sounds like you've possibly missed a step, you'll need to assign the user to the domain workgroup, to do this click the "security" tab in the menu bar > Workgroups> select the domain workgroup > Click "Workgroup Users". if your user is not listed in the workgroup then click "Add User" and select the user.
if you've already done the above then the user may have locked their account, to check and unlock the user select click the "security" tab in the menu bar > Users > locate your user > Edit , If the "User Locked" checkbox is ticked you'll need click the unlock user button.
I've included a link below for further information regarding workgroups and users
Workgroups and users
Thanks
Ranjit