In Windows XP I can open "My Computer" and see all the hard drives. I can also see the explorer.exe process running among other processes in Task Manager. But after opening "My Computer", when I double click on one of the drives to open it, I get the following error message:

Windows cannot find 'explorer.exe'. Make sure you typed the name correctly, and then try again. To search for a file, click the start button, and then click search.

Although I could detect and remove several suspicious files using Malwarebytes & Microsoft Security Essentials, the problem still remains. The interesting point is that if I right click on one folder and select Open or Explore from the menu bar, I can open the folder! but if I double click on the folder, it does not open and I get the above error message. How can I fix this problem? Any advice would be appreciated!

Update: I formatted the C: drive (NTFS), a deep format, and installed a fresh Windows XP on it. I am not getting this error when I double click on C drive icon anymore. But the same error appears when I double click on other drive names. Maybe I should format them too!