I see you have a magnetic hard drive. Was the machine turned on when you abused it? It's possible you "crashed" the hard drive (read about that if you are curious). Crashes are usually not recoverable although you might get some data back with the right tools. It's very unlikely that your hard drive needs to be "reseated". It is held in mechanically with screws. But there are other failures beside the disk that could a failure to boot including the interface electronic interfacing the drive.
I trust you are following good anti-static (ESD) precautions when you open up your machine. You can cause additional damage if not. Again, read about this on the internet.
My next step would be to download a bootable diagnostic program, load it on a CD or USB and run it on your machine. That should give you an idea of what is really wrong. Messing around aimlessly inside your machine is just asking for more trouble. Your best bet may be a good repair shop.