so i just bought 2 umbrella flashes off ebay for $70. they said that the flashes would be triggered off of my on cam flash (or another off cam flash) well they fire but my camera doesnt have any result from them, its like they go off before my shutter catches the image. they cam with what i think are pc cords, but i have a canon rebel xsi which doesnt have a pc port! anybody know what i could do about getting the flashes to work properly or if they have a pc adapter or something? Thanks!