If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
You must kill all 45 terrorist in order to complete the mission and save the hostages. Your night vision scope will become active once the electricity is cut in the building. This should provide you with adequate coverage against terrorist. You only have 3 minutes before the lights come back on and your position is revealed. Good luck!
Use Mouse to interact.