System comes up but no signal to monitor

Hello,

i have a system with an m791g ver1.0 mobo which has been working well for sometime now. dis week on booting the system it was coming up but the monitor received no signal. there is no vga card on it except the onboard one. i also think i noticed the vga onboard port was broken. please any advice on wat to do? i tried it on another system and its still the same thing. thanks