Remote Server and dissapearing files

Our company’s server is hosted by a tech company. We are experiencing a problem when moving files or folders. when a file is either cut or copied and pasted, the entire screen will go blank for several seconds, and close any open windows. Even more distressing we find that when folders are moved, quite often some of the files in them dissapear. We have lost some very important documents. The Server company is of no help.
Can anyone tell me why this would happen, and what can be done about it?