Just out of interest, reading from others with this problem, have you tried going to its location (Fsx) and running Fsx.exe, rather than trying to start Fsx with the desktop shortcut.?
you may want to investigate this as you’ve uninstalled Fsx.
I forgot a step. This is what I did.
The last time I tried to install FSX, and getting the dreaded"Unhandled ExceptionError Number:0x80040702Description: Failed to load DLL: GameuxinstallHelperSetup will now terminate.",Out of frustration, I looked into Disc #2 and found the 'MSXML.MSI'. I clicked it and it ran the 'MSXML 4.0 SP2 Parser and Setup Wizard" (whatever that is)Then, I looked in "C:\Program Files (x86)\Microsoft Games\Microsoft Flight Simulator X" and found the "GameuxinstallHelper.dll"I had then copied, CTRL+INSERT, the DLL.Then went to the "C:\Windows\SysWOW64" and pasted that DLL to that location of which it was missing.I then ran the installer once again and this time FSX loaded completely, without any issues so far.I don't know what exactly was changed or why but, it seems to have fixed this issue.