Hmm, try setting your radar range to infinite... look in your options (F2) under Control Config button, prolly under "Targeting" or "Misc" - look for change radar range key.
For registry, it is HKEY_LOCAL_MACHINE\SOFTWARE\Volition\FreeSpace2 (use Start-Run regedit; DO NOT CHANGE ANYTHING UNLESS YOU ARE SURE WHAT YOU ARE DOING!!! YOU CAN DESTROY YOUR WINDOWS INSTALLATION!! [ie, don't fool with anything except for that key... changes are immediate; no saving. The only thing that might save your butt if you fooled with something else is System Restore Point in ME / XP / higher)