Caryl;
Glad you could sucessfully burn the Trisquel CD.
It sounds like your Mac Graphics Card is incompatable.
You may be able to start it by modifying startup parameters by adding
nomodesetor vesa to boot line .
(esc tab at boot menu (after language selection on Trisquel)- edit
boot line
http://wiki.sugarlabs.org/go/Sugar_Creation_Kit#Set_up_MacBook_to_Open_VirtualBox_automatically_when_you_power_it_on
* Open Accounts preferences
Click Add(+) button to the right of the accounts list
Select an application (VirtualBox) and click add.
* Boot Mac
Mac opens