Oracle Apex ---oracle service instance xe failed message when install.

Solution :

1. Try to delete the service using the command prompt:

1. Click Start, type ‘cmd’ in the search field, and when ‘cmd’ shows up in the list of options, right click it and select ‘Run as Administrator’.
2. At the Command Prompt window, type “sc delete OracleServiceXE” without the quotes and press Enter.
3. Type “Exit” and press Enter.

Hope it helps. 

C:\> sc stop OracleServiceXE                      (to Stop service)

C:\> sc delete OracleServiceXE                      (to remove)