I have this as text from a few years ago and I'm not sure who created the article but here it is. Hope it works for you:
Uninstall FsX
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1. Click on Start
2. Click on Control Panel.
3. Click on Switch to classic view
4. Click on Add or Remove programs
5. Check mark on Show updated at top bar of the window.
6. Select Microsoft Flight Simulator X Service Pack 1 (Accel or SP2 if
they show up on the list as well I would assume – and this is after
already having removed all other add on scenery, planes, meshes, textures,
and any associated left over folders, etc. – FlighT01 ) from the installed
program list and then click on Remove.
7. Now select the Microsoft Flight Simulator X and click on Remove and
follow the instructions to uninstall it.
II Remove the game folder
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1. Right click on Start
2. Click on Explore
3. Click on Program Files
4. Double click on Microsoft games
5. Select the Flight Simulator X folder and press the Delete key on the
keyboard.
III Remove the folder that has saved game content.
1. Click Start, and then click My Documents.
2. Right-click the Flight Simulator Files folder, if it exists, and then
click Delete.
Note: If the Flight Simulator Files folder does not exist, close the My
Documents window, and then go to step 3.
3. Click yes to confirm that you want to remove the folder and all its
contents.
4. Close the My Documents window.
IV Remove the FSX folder
1. Click on Start
2. Click on Run
3. Type %appdata% in the box and click on OK
4. Double click on Microsoft folder
5. Select FSX folder and press Delete key on the keyboard.
V Remove the game from Registry
-------------------------------------------------------------------
WARNING: If you use Registry Editor incorrectly, you may cause serious
problems that may require you to reinstall your operating system.
Microsoft cannot guarantee that you can solve problems that result from
using Registry Editor incorrectly. Use Registry editor at your own risk.
VI Remove the game entries under HKEY_LOCAL_MACHINE
1. Click on Start
2. Click on Run
3. In the box type regedit and press Enter key.
4. Double Click on HKEY_LOCAL_MACHINE
5. Double Click on Software
6. Double Click on Microsoft
7. Double Click on Microsoft Games
8. Locate "Flight simulator X" and delete the folder. Click on yes when it
asks to delete this key and all of its sub keys.
9. Click on edit and click on Find next
10. In the find box type Flight Simulator X and click on Find next
11. Delete the entry that is found and then press F3 to find the next
entry. Keep on pressing F3 until all the entries of Flight simulator have
been deleted.
12. Close the Registry editor.
Note: The above steps will remove the Flight simulator X completely.
VII Please restart the computer.
VIII Clean Boot
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When you start Microsoft Windows with a normal startup, several programs
start automatically and run in the background. These programs may include
third-party antivirus programs and system utility programs.
When you try to run the game, these programs may interfere with the game.
If this occurs, you can use a clean boot to start your computer before you
play a game. This prevents these background programs from starting
automatically. Hence, we will try reinstalling the game in Clean boot
mode.
NOTE: You must be logged on as an administrator or a member of the
Administrators group in order to complete this procedure. If your computer
is connected to a network, network policy settings may also prevent you
from completing this procedure.
1. Click on Start, and then click Run.
2. In the Open box, type msconfig, and then click OK.
3. On the General tab, click Selective Startup.
4. Under Selective Startup, click to clear the following check boxes:
- Process SYSTEM.INI File
- Process WIN.INI File
- Load Startup Items
5. On the Services tab, click to select the Hide All Microsoft Services
check box.
6. On the Startup Tab, click the option "Disable All"
7. Click on Apply, then click on Close, and then click on Restart
Disable any antivirus or system security software (Norton, MacAfee). Also,
if you have any third-party software installed for video performance or
refresh rate optimization, please disable that software.
I Reinstall FSX
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1. Insert the Flight Simulator X Deluxe DVD Disc 1 in the DVD drive.
2. On the first page of the Setup wizard, click Next.
3. Click Install.
. Install Installs Flight Simulator X.
. More Options
On the More Options screen, you can change install location, limit users,
and start Flight Simulator X after installation.
4. Install for all Users, run after install, view Readme, and then add a
shortcut.
5. To change the Installation folder, click Browse, and then select a new
location. . To display free space on all drives on the computer, click
Disk Space.
6. The installation process will start. When you are prompted to insert
different Flight Simulator X discs, insert the appropriate disc, and then
click OK.
After the installation is complete, the game will build scenery file
indexes.
X Download and install Visual C++ Redistributable package
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To download and install Visual C++, please visit the Web site mentioned
below.
http://www.microsoft.com/downloads/details.aspx?FamilyId=32BC1BEE-A3F9-
4C13-9C99-220B62A191EE&displaylang=en
Click on Download on the web page and save it on the desktop. Go back to
the desktop and double click on the downloaded file and try to install the
package and then try installing the game.
XI Restart the system.
XII Download and install Flight Simulator X Service Pack 1
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Download and install the latest Flight Simulator X Service Pack 1. To do
this, visit the following Microsoft Web site:
http://www.fsinsider.com/downloads/Pages/FlightSimulatorXServicePack1.aspx
Click on Download on the webpage, when you receive File Download dialogue
box, then click on save, save the file to the desktop. Go back to the
desktop, open the downloaded file, and try to run the update.
XIII Download and install Flight Simulator X Service Pack 2
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Download and install the latest Flight Simulator X Service Pack 1. To do
this, visit the following Microsoft Web site:
http://www.fsinsider.com/downloads/Pages/FlightSimulatorXServicePack2.aspx
Click on Download on the webpage, when you receive File Download dialogue
box, then click on save, save the file to the desktop. Go back to the
desktop, open the downloaded file, and try to run the update.
This time it worked, and has been fine since.
It may be that that is your only choice.
Hope that's of some help.
I won't put the posters name here, and apparently these instructions are
from Microsoft Support. I do not remember where I saw this. I wouldn't
want the poster to take any blame if something I cut and pasted here is
incorrect. I haven't had to go through this yet myself, so I don't know
how it works, but I'm certain at some point I probably will. Sooner or
later with FSX... I'll fubar something up, done it before, I'm sure I'll
do it again. And if nothing else it's worth a shot if your contemplating a
complete reformat to see if you can save yourself some time and
