.exe executable can't open problem solution

The computer appears in the problem as stated in the question, click on the properties of my computer to pop up a dialog box saying "Cannot find C:/WINDOWS/system32/rundll32.exe", and later want to open some installed software programs but pop up a request for you I chose the dialog box for opening the way, and later I found that the anti-virus software was gone. What surprised me was that I couldn't install the file! What should I do?
Workaround: For the exe open mode, it can be modified by Trojan or virus. Implement the solution for the file.
Scenario 1: First rename regedit.exe to regedit.com or regedit.scr.
Run regedit.com, find the hkey_classes_root/exefile/shell/Open/command key, change the default value to %1 %*, and then change regedit.com back to regedit.exe.
Scenario 2: Save the following content as exefile.reg, double-click to import the registry; or run regedit exefile.reg under pure dos, import the registry. (Note: leave a blank line after regedit4)
regedit4
[hkey_classes_root/exefile/shell/Open/command]
@=/%1/%*
Scenario 3 (only for win2000/xp ):
1, rename cmd.exe to cmd.com or cmd.scr.
2, run cmd.com
3, run the following two commands: ftype exefile=%1 %*assoc .exe=exefile
4, change cmd.com back to cmd.exe
Four: From the new associated EXE file. Open any window (non-IE window), tool---folder option----file type----new ———— fill in “file extension" ----- Click Advanced, select “ Application & rdquo;------- OK in the drop-down menu.