你要保证你完全删除了Step7，直接在添加删除程序中删除Step7是不够的！
完全删除Step7的步骤如下，希望对你有帮助。
QUESTION:
How can I completely deinstall STEP 7?
ANSWER:
It is principally recommended to deinstall the complete Siemens-Software and to reinstall it after the deinstallation of step 7.
The following text describes the procedure.
Warning:
In the deinstallation described the complete SIEMENS folder and all Registry entries of the Siemens software installed on your computer are deleted. If this folder still contains projects, then you must copy them to another directory using the SIMATIC Manager function "File > Save As&". You can also save the data in another directory or on a different drive using the function "File > Archive". Do not copy or move the projects using the Windows Explorer. Still save your GSD files from the directory "<>\Siemens\Step7\S7data\gsd\".
Important:
First transfer your authorizations to the authorization floppy disk provided for this.
1. Start the "Software" via "Start > Settings > Control Panel" and deinstall all the SIMATIC applications.
2. Then restart the PG / PC.
3. Start the Registry editor via the menu command "Start > Run".
4. Enter "regedit" and acknowledge with "OK". The Registry editor now starts.
5. Open the directory "HKEY_CURRENT_USER > Software". There you will find the "SIEMENS" subdirectory.
6. Select this directory and delete it.
7. Open the directory "HKEY_LOCAL_MACHINE > SOFTWARE". In it you will find another "SIEMENS" directory.
8. Select this directory too and delete it. Then the Registry is free of all SIEMENS entries.
9. Close the Registry editor and then delete the complete Siemens directory (<>\Siemens) as well as all the S7 files in the Windows system directory. For this you open the Search mask via "Start > Search > Files/Folders..." and search for all the "S7*.*" files.
10. Delete the SIMATIC folder in the start menu.
11. Delete the data file "simatic.cfg", located in the Windows-directory (e.g. C:\WinNT oder C.\Win98).
Note:
With new operating systems it might be the case, that this file is already no longer there.
12. Delete the data files C:\RASETU*.*
13. Search the data file "citamis.str" via "Start>Search>Files/Folders in the windows directory (e.g. C:\WinNT C.\Win98) and delete this file
14. Additionally, empty the recycle bin.
15. The deinstallation has been completed then.

文档是英文的，我就不翻译了，比较简单，应该很容易看懂。
估计你完全删除step7后，再重装就好了。否则原来在注册表中残留的信息会影响Step7的重装。