"Cannot find Country.Sys file"

Please excuse this repeat posting, but upon startup, I get the subject line
as a message when the screen is black. A guy kindly replied a month ago
saying that this file is to be found somewhere or other but this meant
little to my unexpert mind. I'm not seriously into computers and so I would
like to ask 1) why is it asking for the Country.sys file? 2) does my
computer need it? and 3) why did it go missing in the first place?
If my machine does need it, is it an easy task to rectify the problem?
Any advice appreciated. Chris