Image start to shake after a few minutes.

Hi,when I start to use my projector and pass a few minutes the image start to shake until it's gone. I found the heat sink behind out of it's place and I had to put a glue and heat compound to pu it back on it's place. Now it's work for a few 10 or 12 minutes and start to shake again, it's gone but the image come back and so on. Any idea? What is the name of the that project the image throughout the lens? Thanks!