Can anyone help me with this because this is driving me mad.

i plugged in a usb microphone, turn off the pc and now when turned on nothing appears on the screen so i cant even enter the bios.
the fan runs, i can hear the proccessor running, the fuse is fine and there is power.
the usb port i used was built into the bored so could that have blown the motherbored?
if not what else could it be?

thanks alot to anyone who is willing to help me out here.

pc specs.
pentium 4
windows xp
mother bored- L4S5MG3 - ECS Elitegroup (http://www.motherboard.cz/mb/ecs/L4S5MG3.htm )
make: a local reliable company assembles them themselves.

oh yeh and i have tried differnt monitors and leads.