Shield does not work

[masarada]

I am trying to beat the invisible lizard kinda boss-stalker (in the water room)
after some time it starts throwing bombs after climbing down the pillar. At this point I find at times, the shield does not come up, eventhough I am pressing frantically at button Y.
Why doesn't the shield come up ?
Is there a limit to the number of times, the shield can be brought up ?

[Saito]

If I remember correctly, you have to hold it in...

If its wrong just disregard that.

[T Virus Licker]

You mean the Stalker. Yes, the shield has limited times of use. If you look at Hayden's right arm you'll see some lights. That's the guage for your bio-energy. If you don't see any, it needs to recharge. It don't take long for a recharge of your bio-energy, but you can't use your shield, or pulse till then. All you have to do is wait for at least one light to come on, not all three.

If you mean total limit times for the shield, no there is no limit. You might have a problem with your controller button if the shield is not coming up.