no picture on the monitor

i turned on my pc the other day and the computer it self is whirring
away and making all the usual noises but on the screen is just a "no
signal, check cable message"

the lead is in fine at the back and i have checked the monitor on
another computer and it has worked fine. i am using on board graphics
so i thought i could get a graphics card to solve the problem but i
cannot turn off the on board graphics in the bios without a picture on
the screen. also there is not a jumper on the mother board to do this
physically.

is it time for a new motherboard?

all help will be greatly appreciated:)