I've gotten myself in some pretty deep ****. I agreed to fix a friends old gateway computer, and after opening it up and doing tests on the cpu, ram, etc, i made it worse. When the laptop came to me, the fans would start and you could hear the computer running, but the screen would stay completely black when you turned it on. Now, the computer doesn't respond to pushing the power button at all, except for a slight change in pitch of the sound the power board makes as you hold the power button down. Any help would be appreciated because this guy is waiting for his laptop and all I've done so far is make it worse.

You should of just tested to see if some level of the LCD was experiencing issues via using an external monitor. No signal to an external monitor would likely imply a defective system board or video card. However, receiving a signal to the monitor would suggest that some level of the LCD and or it's connection to the motherboard has failed (commonly just the inverter).

Anyway, pull everything back apart slowly, disassemble it to the exact level that you disassembled it before. Then, put it back together, slowly and make sure each and every device/cable is fully seated. Sounds like perhaps something isn't connected properly.

Yeah I connected it to a vga monitor right when i got it. nothing. it was black just like the laptop screen. I ordered the video card on the gateway website, that it says the the laptop has, but i think the video card is integrated because I couldn't find it when I opened the laptop up. If the video is indeed integrated, then i could get a new motherboard for it, but that would be $150 out of my pocket.

...As far as I know, nearly all laptop video cards are integrated. They don't occupy an expansion slot as they commonly do with desktops.

The best route for you to take now, is to replace the system board. That would of been the case despite your error (if there was one). Explain the situation to your friend and it will be out of their pocket, not yours. Why should you pay for a system board that needed to be replaced regardless?

Check it out, part by part. From our experience on that series of Gateway laptops:
Faulty/dead power adapter.
Loose/defective power jack that the adapter plugs into.
The video card is installed from the bottom, has a thin plastic wrap, and doesn't look like a video card.
Consider memory. If a memory module has gone bad, it may have the symptoms you describe.
The motherboard seldom fails.
CPU fan commonly fails, but is inexpensive to replace.
Be careful when splitting the case.
CMOS batter could be dead. It is under the keyboard.
Replace what you can... hard drive, memory, power adapter.
Remember that you probably did not do this. It came to you with a component in its death throes... it just finished suicide under your watch.

Okay, i will find a cmos battery and I'll check the dc jack. It's reassuring that you said motherboard failures are rare in these machines because that would be the most expensive and that is what I was worried about.

Taking into considering the fact that a large portion of the internal components are integrated within the motherboard, if any of them fail, consider that system board failure and it'll probably need to be replaced.

On a desktop, yes, motherboard failure is rare. On a laptop, it's not so rare at all. Components on a laptop's system board fail at a higher rate than "rare" that's for sure.

In an attempt to replace the cmos battery, I broke the socket for the battery off of the motherboard. It's a bummer. The contacts are pretty big, though, so i think i could solder it back onto the board. Would that be safe to do and if so any tips to prevent damage to the motherboard??

Should work if you are skilled at soldering. I would use a "cold solder" instant-on unit.
Surround the solder area with standard damp heat absorber.