Problem installing and removing CiviCRM on a Joomla 3.6.3 site
If the CiviCRM component does not install correctly 

(for example you get a blank screen instead of the confirmation page), 

delete the ~/components/com_civicrm and 

~/administrator/components/com_civicrm and 

~/media/civicrm directories manually 

and then try each of the following before attempting to reinstall:

Please refer to the below link : this is for 4.5 but still this should work for 4.7 too 

https://wiki.civicrm.org/confluence/display/CRMDOC/Joomla+Installation+Guide+for+CiviCRM+4.5

I guess this helps !!!