Plane is in c:\program files but not in Flight Simulator X

A question for "tomthetank". I am new to flight simulator x. I have read your imformation about downloading and installing airplanes and have followed them. My problem is, the downloaded plane shows up in c:\program files\microsoft games\microsoft flight simulator x\simobjects\airplanes but does not show up in flight simulator x. What am I doing wrong? I have tried it several times with no avail. I have downloaded several other airplanes with no problems but I am stuck on a few others that just won't install into flight simulator x even though they are in the c:\program files.... Please help! Thank you, dutchmen94.