Microsoft has a method to easily disable certain ActiveX controls, using a "kill-bit".  It is documented at http://support.microsoft.com/kb/240797

The "kill-bit" for Flash Player is documented in http://kb2.adobe.com/cps/190/tn_19091.html

What does that mean?

Flash  Player may not be working on Internet Explorer, and the 'Shockwave  Flash Object' add-on may not show up at all.  Most likely because the FP  ActiveX has been "kill-bited" by some anti-malware app.

How to check and remove the "kill-bit"?

WARNING!   Fiddling with the Windows Registry may render Windows or installed  components unusable.  Always make a registry backup or a System Restore  Point before attempting to manually change anything in the registry!

• open the registry editor: Start | Run | type regedit.exe
• navigate to this registry key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{D27CDB6E-AE6D-11CF-96B8-444553540000}
• if that key does not exist, then the "kill-bit" for Flash Player is not set
• if it contains a DWORD entry with the name Compatibility Flags that has any value other than 0x00000000, then the "kill-bit" for Flash Player may be set
• to remove the "kill-bit" do any of the following
  • change the value from 0x00000400 to 0x00000000 (right-click | Modify | change value data to 0)
  • or  delete the registry key (HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet  Explorer\ActiveX Compatibility\{D27CDB6E-AE6D-11CF-96B8-444553540000})  completely
• close the registry editor when done