Ok, if the space bar is the only thing that isn't working, you need to make certain the cable is seated properly. It is possible that the laptop was jarred and the cable came loose. Youtube how to take your particular laptop apart if it is out of warranty.
If you have reset the software and no changes, it would have to be a physical problem. I would go and get an external keyboard first and see if it still duplicates. If it does not , then you know the BIOS of the Laptop is good (as it is correclty receiving and correctly responding to hardware requests as expected). If it does duplicate, then the BIOS of the laptop has been corrupted and need a new load (as the new keyboard is repsonding the same as the other one, bios in common.)
The easiest quickest way to t-shoot this problem without taking apart your laptop, is to go and get a usb keyboard and plug it in to see if it works as expected. I got one at "BIGLOTS" for under $10(US).