My computer keyboard starting doing its own thing

I have a Satellite M35X. I use this laptop for work and personal use. It was purchased January 2005, so it’s 18 months old. Recently, I purchased Scan Disk to back up my documents file on a chip that you can carry around your neck, — I don’t know the technical name for what they call this. The day I plugged this in to a USB port, 20 minutes later when I was working in Microsoft Word, my computer keyboard starting doing its own thing. If I hit the shift key, it would take off typing “n” across the page or the backslash symbol. It would reboot but I could not get past the password screen. When I started to enter my password – the touch pad still works well in moving the cursor to an area. It would permit me to enter 3 characters, then it would return wiping the display out and back to reentering again. I purchased a new keyboard and replaced the old. The same thing occurred. I purchased an external keyboard, and unplugged the laptop’s keyboard. For the first 4 hours everything went well, then it did the same thing. When I went into Word it would start typing capital “b” across line upon line. Hitting Escape did not stop it. Holding down the backspace key just caused it to delete the last typed letter, but as soon as it was released, it would continue across the page. Sometimes it would type three characters on a line then return and start with a backslash symbol and type a couple more alphabets on that line, then return and start with a backslash again and a few more characters, return again, and do the same over and over. The alphabet typed on the lines were not always the same – it liked a capital “A” and “n” quite often. When you then go into Microsoft Explorer it will not let you type in the search bar or the address bar but inserts backslashes, continual, never ending Since the laptop keyboard has been replaced, and an external purchased and plugged in, it is not the keyboard, but must be something in the computer. HELP! Any suggestions????

According to the description you’ve provided, I would assume that the keyboard is bad, but you already replaced it. That is a very strange problem. I assume that it might be a software problem.
You can try to reinstall the keyboard drive. Open the device manager and find the keyboard line. Click on the plus sign to expand it. Right click on the “Standard 101/102-Key or Microsoft Natural PS/2 Keyboard” line and click on uninstall the driver. After you reboot the laptop, Windows will reinstall the driver automatically. Try it first – it might help.
Also you can try this. Revert the operating system back in time when the keyboard was working properly. You’ll have to use the system restore utility. Go to Start – All Programs – Accessories – System Tools – System Restore. Choose date and time when the keyboard worked fine and run the restore. This process will revert only system files and you shouldn’t loose any personal data.
If it still doesn’t help, you can reload the operating system from a recovery DVD. It will take the laptop software back to original factory defaults. When you re-image the drive all data on your hard drive would be erased. BACKUP all important files before you run the recovery DVD. This process should eliminate any software related problems.
One more thing. Try to re-flash or update the laptop BIOS. May be the BIOS is corrupted and it causing the keyboard problem.
If it still doesn’t help, then I would assume that the keyboard controller on the system board can be bad and the system board has to be replaced.