PC BOOT PROBLEM?

I have just reconditioned my P3 computer with a new 370 motherboard Via GA-6VMM, A P3 1.1GHZ CPU, larger hard drive 8.5GHz to a 20GHz, more and faster memory from 128MB 100 to 640Mb 133,and added a DVD drive along with the CDROM.
I have checked and re-checked all the connections, made sure the memory is fully home in its slots,that their is no shorting issues with the board and that the jumper settings are all correct.
However when I switch it on I see the Motherboard light comes on, the hard drive initiates, the CDROM and DVD both have power and the drawers open and close,the Floppy light indicates the drive ready and the CPU and chassis fans are both going.
The monitor however remains blank and the machine does not boot?
I have built computers before and this one should be working perfect everything as it should be but still nothing happening
?
Can anyone shed some light as to what the prob could be.

Andy Milne
March 2006