On your hard drive, there are two plug you need. One is the SATA cable, the other the power cable.
The power cable is a thin, flat plugin, and SATA is a flexible cable that plugs into the motherboard and into the hard drive. Unless you have IDE hard drive, in which case, the power is a 4 pin plug, and the cable is a flat ribbon, usually colored blue on the end to the mobo.
Um, how did you manage to disconnect the hard drive? The cables that got caught by the chair would have to be hanging down pretty far to get in the way. If you pulled out the power cord, then your power would go off and if your hard drive was running at the time, which it was, then you could have corrupted it. But I don't see how you could have pulled out the plugs from the hard drive.
If you have more then one hard drive in your computer, make sure that the hard drive you want to use is chosen is bios, as number 1, so that when you start up, you will start up on the hard drive that has the system files on it.
I have a computer with three hard drives, and once I switched hard drives around, and so the SATA cables were on different drives then they were previously, (SATA1 on number 2 drive, SATA 2 on number 1 drive, etc.) and the bios was then numbered wrong, and my computer would not come up.
Try setting the numbers right on the drives, before you re install anything. That might be all that is wrong with it.
otherwise.....
If you can get into the bios, set your computer to start on CD first, then put in your Windows cd.
Try installing Windows on Repair only, (not recovery ). When Windows setup gets to the point where it asks if you want to repair or do a clean install, choose "enter" and do a repair. Do Not do a clean install, it will wipe out your drive. A "repair only" will clean up your registry and hopefully repair any errors you might have. You should have a backup of your files before you do this, but in this case, I don't see how you can. Just do not choose a clean install.