urgennnnnttt monitor help!!!!

i hav d following rig

i3 540
asus p7h55mlx
transcend 4gb ddr3
zotac gt440
iball sprinter 450w
iball bullets cabinet
viewsonic 1280x1024

i recently reinstalled windows 7 ultimate x64.it worked properly.aftr i shut it down i dint use it until i replaced it with a new compaq r210.
i plugged it in but the display was not showing up.
so again i used my old monitor...
now the display is not showing up in my old monitor also.....
plzzzzzzz help!!!!!!