Significance (research gone wrong, please help!)

#1
my convinience sample size was 148, i distributed questionnares (made up of rating scales) to all those in the sample. i had a response rate of 25. is it true to say that because i used a convinience sample, the results cannot be tested for significance?

if this is not the case, when people are answering yes/no to a question then what test can you use to test for significance? :confused: