Jump down to the next floor to continue on with the fight. You will find a Neutron Assault Rifle at the corner. Grab it if your wish and take the energy lift up to the next floor, where you will find the skinny ramp on which you were ambushed. Cross it and access the control panel by the large hologram. This will cause the power to reactivate for the area and bring the weapon's targeting system back online. Your allies will link the artillery right into your optical targeting system, meaning you'll soon have anew toy to play with. Proceed through the door in the back of the area and rush out to the plateau in the back. You will see a Marauder artillery cannon laying waste to your forces. Hold RB and point the reticule at the Marauder. Hit the A button to initiate an aerial assault on the designated location. The Marauder will go up in flames with just one shot. You will now have to deal with the footsoldiers below and to the right. You can gun them down from your elevated position without too much trouble, but wouldn't it be much more satisfying to wait for the artillery's cooldown to recharge before tearing them all apart with another airstrike? Yeah, thought so.
With the enemies here dispatched, head back to the engine room. Before leaving the plateau, be sure to check the back left hand corner for ammo and an Energon Cube for health. Grab it and drop down to the level below, the same area that you just shelled. You can find more ammo and health down here if you need it. If not, proceed towards your waypointand up the ramp to the upper level. Head through the opening door to the right and proceed down the hall to an elevator. The elevator will lower you down to the engine room. Follow the ramp up to a separate level and enter the room ahead. Pull the switch back to funnel power through the wires overhead an into the massive door in front of you. Proceed across the walkway and through the door. Approach the large cylindrical metal piece on the other side of the rom and it will open for you. The path ahead of you will begin to shift unpredictably. Simply follow the path as it opens up for you; it won't always be straight ahead, so always look around for new paths opening themselves up.
When you reach the end of the path, you will have to squeeze through a small gap in the wall. In the next room, the power will go out. Approach the yellow door and hit X to force it open. Proceed down the hall. You will see Autobots being attacked, but you won't be able to help them. Don't get too distracted by this; smash the chest behind you and take the cash before proceeding down the hall. Blast the red gate out of your way and pick up the Scatter Blaster if you want it. Starscream will await you in the next room with a few of his lackeys.
Starscream won't have the guts to fight you himself, so he'll send down several of his Shotgunners. These enemies are absolutely deadly up close; their Scatter Blasters are for whatever reason much stronger than yours is. Leave the room through the hole you blew in the gate and let the Shotgunners come to you. Funnel them through the opening and go for head shots as they rush you. In the empty room ahead, you can find ammo for your primary weapon and health. Run to the top of the stairs when you're done and press X to pry the door open. Smash up the barrel in the back of the room for some health, and then take the energy lift up to the next level, where you can find more health if you need it. When you're ready to proceed, head towards the waypoint marker, which is located up the stairs and to your left. You will have to boost over a gap, where you will find secondary weapon ammo and a Molecular Grenade device. Pick up the power conduit here and install it in the console at the end of the room. You will find a Chaos Rift Combustor secondary weapon hidden behind the barred-off door. Pick it up if you want your secondary attacks to pack a real punch, and then finish proceeding towards the waypoint.
Leave the room through the hall to the left, stepping over the deceased Autobots as you go. You will emerge outside to find that the Ark is still standing somehow. Access the store in the center of the area before proceeding, as upgrading your weapons and buying new gadgets can be incredibly helpful at this point in the game. You should have just enough money for a few decent upgrades. Perceptor will tell you that you need to use another artillery strike to clear the way ahead. When you're ready to proceed, head up the ramp in the back of the area. You will see a large hologram of Megatron ahead of you. He will be giving a speech to his troops below. Give them a rude surprise by ordering a strike on their position, wiping Megatron off of the screen and blasting all of his minions out of existence.