I see your picture, and I see that IF you have adequate signal to TRIGGER the sweep, it will not trigger. Trigger light is OFF. Reason: Your signal? is on CH1, your trigger switch is set to CH2 (use CH1), and the trigger level looks to be FAR from centered (center it), and Low Frequency Rejection is ON (best to use use AC, or DC unless you have a good reason).
What is your signal amplitude, and frequency??? Please correct the settings, and try again.