• Check whether the power switch on the back of the host computer is opened.
• Check whether the starting operation is correct.
• Check whether the source power is sufficient.

• Physical damages have occurred to the hard disk.
• The system guiding is abnormal.

• The hard disk error will lead to repeated hard disk check by the DVR host computer, thus causing slowly starting-up.

• Please check power supply of the host computer. After hitching a lot of hard disks, it’s possible that the host computer starts up repeatedly due to insufficient power.
• Please disconnect the gridline, and then check if the machine operation is normal. Network with serious failures is also likely to lead to repeated starting-up of the host computer.

• Check whether there is anything wrong with hitching of the hard disk, and change the failed one in time.
• Whether the ambient temperature is high.
• Whether there is any heavy-current device near to the host computer or the circumscribing video device. The heavy current impacts the video cable, and make the host computer fail to work properly, thus leading to system crash.

• The host computer is unable to identify the poor U-disk due to its poor compatibility. It’s recommended to test more than one U, or to use new-brand U-disks.
• The USB port contact is poor. During updating, the voltage fluctuates dramatically.

• Check whether the video input, DVR host computer, invigilator or the TV set system is
  absolutely consistent. If not, please set the invigilator or the TV set system option in the automatic
  identification state.

• Check whether the invigilator power supply is opened, and whether the invigilator’s brightness is in its lowest condition.
• Check whether the video cable is properly connected, and whether there is anything wrong in the circuit.

• Whether the video cable is short or broken, or whether there is cold joint or poor connection.
• The video cable bears the power interference. The video cable can extend wire along with the heavy-current circuits. Meanwhile, please select good-quality shielding lines.
• Within the whole system, only single point earthing rather than multipoint earthing of the central machine can be applied. Otherwise, there will be common mode interference. Please connect the DVR host computer to the ground with the grounding screw on its back.
• Check whether aging occurs to the camera, the invigilator or the circuit.

• Whether the output/input video parameters have been adjusted properly in the host computer’s menu?
• Check that everything is well in the connecting lines.

  The image distorts, becomes flickering, Distortion, flicker and color cast occur to the image when using the computer’s display?

• Make sure that the VGA connecting line is properly earthed with the host computer.
• High working ambient temperature or poor radiation of the DVR host computer cause abnormal operation of the VGA display chip or abnormal parameters of related circuit.