High pitch humming sound on boot

put together my friends computer last night and ran into a snag. the first time we turned the computer on after putting everything in it wouldnt post, but we realized we had forgotten to connect the pcu 4 pin power connector. so i connected it, and then rebooted the machine and it posted but we didnt have the cd to load windows in the drive at the time. a short while later the monitor just completely lost the signal, and now every time we boot the computer there is a high pitch hum that comes out and doesnt stop, and the monitor still wont get a signal

specs are:
antec 900 case
ocz 600w psu
gigabyte 965p-ds3 mobo
e6600 cpu
evga 8800gts card
2gb corsair xms ram pc6400
400g sata hd

any help would be appreciated, thanks in advance

I would test the monitor on another PC to see if it works.

It would also be a good time to see if the computer will boot with the minimum of computer parts in it.

the monitor worked the 2nd time we booted the system, so im almost positive that it isnt the monitor