First, make sure you're looking in the right place for your profile pic. Please see:

I chose a profile pic in the Weblog Editor, but it didn't appear when I clicked "Submit"...
http://help.xanga.com/profile-whereentrypicshows.htm

If you're looking in the right place and still don't see your default pic, then you may not have a Default Profile Pic. If you haven't specified a Default Pic in your Profile Picture Manager, then every time you choose to show your "Default", Xanga will show no picture (in a sense your default *is* no picture).

If you want to use a specific pic for your "Default":

• First go to your Profile Pic Manager:
  http://www.xanga.com/private/profilepics.aspx
  
  
• Then find the pic you want to make your Default, and click the little "No" link over in the last (right side) column next to that pic.
  
  
• When prompted, "Are you sure you want to replace your current default?" Just click "OK" to turn that pic into your new default.