Davey............this should fix ya

In This case, you will need to go into the system registry and remove a few registry keys. Be very Careful when doing this. Make sure you follow the instructions completely.
1. Delete the games directory. By default this will be C:\Program Files\EA Games\Medal Of Honor Allied Assault. Then delete MOHAA from the start menu as well. By default this is Start->Programs->EA Games->Medal Of Honor Allied Assault
2. Now load the registry editor. Go to Start -> Run -> type in "regedit" (without the quotes).
3. There is a registry folder that causes this and must be removed. It is found in:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\Curr entVersion\Uninstall\
You must then select and delete the folder name below found in that above location:
{0DEA94ED-915A-4834-A87E-388D012C8E02}
Delete this folder, then close the registry editor, and reinstall the game normally.