Check the SQL Agent log to see if there is any related warnings or errors.
Check the SQL Agent log to see if the Agent service was running when the job was suppose to run.
Try manually executing the job - not the t-sql itself but the job.
Make sure the schedule is also enabled and set correctly - look at the dates, make sure there is no end date, make sure it's not set to run once or in the past.
Look at the job activity monitor (in the jobs folder in SSMS) and see if the next run date and time is listed.

Sue