When i went to the grad school, the graduate office used to take the annual evaluation of the grad student to make sure if the assistantship should be continued or not. In our school, under 3.0 GPA in the first semester would give a warning and suggests what we need to do. That means, if we improve the GPA in the next semester and if the CGPA is above 3, then we would not be put on probation. Since this is your first semester, the school should not be so harsh on not providing the assistantship. THe best way to figure out the option would be to talk with you major advisor (if already assigned) or talk with the program assistant of the department for the possible action you can take.