There's no need to worry about not having the SP2 or Acceleration installed, the installer will obviously check for this and will alert and refuse to continue if they are missing.
As discussed in many other threads, your problem is likely the usual problem of your MS VC++ runtimes libraries begin corrupted. You can try downloading and installing the Stand-Alone Addon Manager for FSX AFTER installing GSX. Since the Stand-Alone Addon Manager requires a different version of the runtimes, we can hope this one is not corrupted too in your system.
