is there integrated graphics on mobo?
If yes, disable in BIOS [hook monitor to mobo vga port].
If there isn't onboard vga, then, have you got a spare vga card lying around that you can try?
Does the system beep when you switch it on, and does the hdd led flicker as if windws is loading ok?
What do you see and hear?
Does the computer make any noise at all when you try to boot up???
more info pls