Hi Mohammed.
For this issue we would recommend contacting Promethean technical support directly to help resolve this issue.
You can either contact us via phone or through filling out a form on our knowledge base. When contacting us please quote reference number 357425, please have your serial number of your PRM-35 projector to hand and please obtain a photo of the pixel issue.
If you have any questions, please do not hesitate to get in touch.
Adam
Promethean Technical Support.