will not send print job

I have three Dell boxes that refuses after a period of time to send print jobs. They are sending print jobs from a print database to either a Markem printhead or a print head used to print on plastic bags. I have checked the pc,database, and printheads and all seems fine. The only way I can get it up and running is to move the database into another dir. and load an image to c:. Once done it runs fine for a couple more months. Ideas?