Question Cable not connected

Jan 24, 2020
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Just assembled my computer , and I get "cable not connected" on the monitor . I have tried another monitor /cable / dvi - vga connector and also another Vga card but the same problem . Can anyone suggest a solution . The computer fires up , all 5 fans and sounds like the drives are working . There is no beep from the PC though .
One question that sounds dumb to me , is can the monitor OSD be accessed without a display from the PC because none of the buttons apart from the on / off do anything ( I have a vague memory of them not working before I rebuilt the PC ) .