I am trying to configure apache for https service in xampp , i am almost done i am jsut struggling with that virtual tag in which i have give information about my self-signed ssl-certificate and key file , apache is not allowing me to use port number 443 in virtual tag even though i have no other service is running on this port , instead its working very well with any other free port like 55000

<VirtualHost *:443>
# Server Certificate:
SSLCertificateFile "C:/xampp/apache/bin/mycert.crt"
# Server Private Key 
SSLCertificateKeyFile "C:/xampp/apache/bin/mykey1.key"
SSLEngine On
ServerName localhost
DocumentRoot "C:/xampp/htdocs"

error :

Error: Apache shutdown unexpectedly.
3:36:52 AM  [Apache]    This may be due to a blocked port, missing dependencies, 
3:36:52 AM  [Apache]    improper privileges, a crash, or a shutdown by another method.
3:36:52 AM  [Apache]    Press the Logs button to view error logs and check
3:36:52 AM  [Apache]    the Windows Event Viewer for more clues
3:36:52 AM  [Apache]    If you need more help, copy and post this
3:36:52 AM  [Apache]    entire log window on the forums