I bought a damaged not working 2008 Macbook Pro from Ebay. I have replaced the battery, added a new SSD drive and upgraded the Ram. I bought a bootable usb drive containing El Capitan and it is recognised by the machine, it begins installing the OS, it starts of with 13 minutes to go, then progresses until there is one second left, then the machine shuts down. When i restart I get the message "This copy of the install OS X El Capitan application can't be verifie. It may have been corrupted or tampered with during downloading"