The following is generally used to fix activation issues with FSX and/or Acceleration. However, it hasn't worked for all, but worth a try:
- Close FSX and run Registry Editor (press Windows key + R and type regedit and Ok)
- Expand the following registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class{4d36e967-e325-11ce-bfc1-08002be10318}
- After you find the folder, double-click Upperfilters on the right side.
- Delete any value there and type in PartMgr (note, this is case sensitive; type it as shown here) and click OK.
5. Close Registry Editor and reboot Computer.
- Start FSX and check whether the Activation box comes up. If so, re-insert your Product Key. Hope this helps you.