black screen with blue box sayin as title shows sometime on pc and have to reset,any ideas?>

 

Usually means that your graphics card is outputting a resolution the monitor can't handle, too high a refresh rate if the res is ok, or maybe a dodgy connection in your cable that means the monitor is missing something (that would be likely if you have not changed anything recently).

Try wiggling the cable at both ends to see if you have a bad contact.