The next step that the technician should do is to have the user unplug the heater. This is because the heater may be causing electromagnetic interference (EMI) or radio frequency interference (RFI) that affects the signal transmission between the computer and the monitor. EMI and RFI are types of noise or distortion that can degrade the quality or integrity of data signals, especially in analog connections such as VGA. EMI and RFI can be generated by various sources, such as power lines, motors, fans, heaters, microwaves, radios, or cell phones. EMI and RFI can cause various symptoms on the monitor, such as flickering, ghosting, blurring, color shifting, or no display at all.

To troubleshoot EMI and RFI issues, the technician should follow these steps:

Identify the source of the interference. In this case, the heater is the most likely culprit, as it was added recently and is located close to the monitor or the cable.

Eliminate or reduce the interference. The technician should have the user unplug the heater or move it away from the monitor or the cable. The technician should also check if there are any other potential sources of interference nearby and remove or relocate them if possible.

Test the monitor. The technician should verify if the monitor is working properly after unplugging or moving the heater. If the monitor is still not working, the technician should try other troubleshooting steps, such as checking the display settings on the computer, ensuring the VGA cable is connected properly, or replacing the monitor.