Half-Life Generator/ Opening the gate Level tip

 Do not go downstairs to power the generator before going to the control room to interact with the guard first.

If you don't to talk him first, YOU WILL BE STUCK THERE. It's a bug.

"Main power is not on."

The gate will NOT OPEN if you don't talk to the guard first before you go downstairs. Don't do what I did, the only reason I know this is because of Youtube Comments sections.