Samsung monitor keeps saying "check signal cable" ?

there is a floating box on my Samsung monitor screen saying "Check Signal Cable."
what does that mean ? i just turned on my computer and the monitor was not connecting to the cpu. it turned on, but it did not connect to the cpu. it was working fine this morning when i used the computer. what do i need to do? help please

its the microchips NT68F63L problem on vga board. you need to open monitor to solve the problem. there are more than 3 ways how to repair. Can you open the monitor ??
or
if you want there is manual how to repair samsung monitors with this problem you can find on ebay: Repair manual Samsung monitor 710n, 913v, 510n and more, Item number: 220389041052.
it shows step by step reparation process.