Screen not turning on

I have no idea what I did wrong.

Took apart my laptop (see signature/system specs) to get the part number off the fan and put the computer back together as normal. Turned it on and voila, no display. Don't know why. Rechecked the connection of the display cable a few times, and still no display. I'm wondering if maybe I damaged the cable or the system board. The computer turns on though, just no display!
Took apart the lid to check the screen. Firstly, HP's construction continues to amaze me. These things are built like tanks for sure! Secondly, there's no visible damage to the screen or any components inside of the lid. Going to put it back together and test the screen one more time, and if that doesn't work, I'll test with an external monitor to see how things work out...

I know, vague, but I'm kinda stuck/lost here.


Help?

External monitor didn't work.

Also noticed there's no HDD activity when I turn the computer on, either. So, the lack of GPU and HDD activity makes me wonder if maybe the CPU got damaged.

I found a new motherboard on ebay for $100, but also found a used Asus U56E laptop (i5, 6GB, 600GB) on Craigslist for $250. All that's wrong is a bad wlan module, which is an easy enough fix. Since I need a computer tomorrow to get working on finishing projects for school, I'm going to buy the spare, order a new mobo for mine, replace the bad WLAN module in the spare, and sell the spare again for the same $250 price.

Unless this is just a horrid idea and I should either not buy a spare laptop or not buy a new motherboard...

I went ahead and ordered a new motherboard. If it doesn't work out, then, well, I'll keep at it until I figure it out.

I wonder if all I did was damage the wire connectors for the display and HDD, and ordering a new motherboard was a waste. Well, we shall see, huh?