In desperate need of help with Prototype

I have a PC, and I'm able to run Prototype with no problem. My question is:

In the mission called Altered World, I'm able to deactivate only two of the viral detectors, but when I proceed onto the third and fourth, no matter what I try, the detectors don't get deactivated. I need to know if this is a glitch, a general problem with the PC version, or is it that I'm missing something here? What am I doing wrong?

Please help. I'm enjoying the game, but I don't want to be stuck here!!!!!!!!

Thanks in advance!