HP 6300 pro Multiple Monitor Issue

Hello, 

In office we are using 3 hp 6300 pro with 4 monitors for each. In each pc we have 2 output from graphic card, 1 from dvi and 1 from vga on board output to monitors. The problem is after the  every restart and normal starting process we can not see the screens  till unplug and plug the dvi cable (the screens are black till that). How can we solve this 

Thanks