NIHILANTH on half life

[the gurn]

Spoiler: Click here to view

Hey im stuck on NIHILANTH in half life i blew crystals and its got green rays and blue rays with green dots coming out of its head, im just wondering if im doing the right thing to kill it and this happens to everyone before he dies cause ive been shooting it for almost an hour and it still not dead any help please? and i am doing the right thing with the signs its showing now

[Bushmeister]

Errr, being slightly drunk, I'll spoiler this as well (though honestly, who the hell hasn't played through the original Half-Life?)

Spoiler: Click here to view

After you shoot at Nihilanth/the nodes around his head enough, his head should pop open. There is a teleport that will throw you into the air just above him - just fall into his brains to kill him and clear the boss.

[the gurn]

Spoiler: Click here to view

well thats just confused me even more sorry i forgot to say its the ps2 version dont see where the teleport is though any help please?

[Bushmeister]

Spoiler: Click here to view

Let me restate what I said:

Start by shooting the three yellow crystals around his head, then shoot at his head until it pops open. Then use the jump pads around you (should be easy to find those) to jump over his head and fire into his brain until he dies)

[the gurn]

Spoiler: Click here to view

sorry to bring this up again just ive shot everything i have into its brain and its still in mid air with green and blue eays coming out of it and green dots coming out its brain ive been shooting its brain for 3 hours now am i doing something wrong?