Changing the glow plugs is meant to make it start better right?...lol just check the connections on the glow plug ends on the lead that connects them all and to where it connects to the wiring loom if you disconnected that while changing.

My car didnt start one time before because i had removed an earth ring on it and the glow plugs stopped working so check any wiring that you have been fiddling with. When you turn the key to the 'pre' start stage does the glow plug symbol come up on the dash still?