Problems when renaming typically arise in two cases: when the original file name, you need a program or OS and in violation of its expansion. The last case in that case if the computer disable extensions.
To enable the showing of extensions, open any drive or folder, select the menu "Tools" - "folder options" - "View". Remove the bird from the line "Hide extensions for known file types". Click "OK". Now you see all file extensions.
Remember what the extension was renamed from the file and restore it. For executable files is often the extension *.exe, to documents - *.doc or *.txt. The pictures usually have the extension *.jpg, music files - *.mp3. If the problem was related to incorrectly set file extension, the file will again begin to run. In the future, renaming a file, leave the extension untouched.
If you change the file name has led to the fact that some program has stopped running, note the message – it usually indicated the name of the file that no program can find. Knowing what the file was modified, you'll be able to bring it to its original appearance.
Important system files are usually cannot be renamed or modified, the operating system prevents this. But you can change them by booting from another OS or using a Live CD. If the changes had a negative impact on the computer – for example, it refuses to boot, you should in the same way to recover the original files. Before changing important files, don't forget to make copies of them.
If you could rename or delete some important system files and the OS refuses to work properly, and the original version of the files is not preserved, try to recover the files from the installation disk. To do this, run the Windows installation, wait until you see the message: "If one of the following copies of Windows XP is damaged, setup can make an attempt for its recovery".
Pressing R will start the recovery process the source files. Your data this process is not affected. After restore, restart the computer, performance of the OS will be restored.