For general troubleshooting tips: see our Troubleshooting Guide
You may need to change one or multiple settings:
Scan Speed
Detector (LEI, SEI for SEM mode)
Voltage (0.5kV-30kV)
Probe Current (typically 7-11, or higher for EDS)
Focus Depth-Resolution
Current (typically 20uA)
Imaging Mode (LM, SEM, GB-H, GB-L)
If you change settings (voltage, probe current, focus depth,) you will need to realign the beam (focus, aperture, stigmators.)