Question: I have a HP ProBook with Windows 10.

My keyboard just started acting super strange. When I press certain keys (shift, arrow keys, etc.), it acts weird; however, all the letter and number keys work fine.

I went to a laptop repair shop today and they said it seems to be a software problem.

They advised me to install Windows 7 instead of Windows 10 because they thought the keyboard driver in Windows 10 is defect or not compatible with my computer which came with Windows 7 pre-installed.

The weird thing is that it worked for a long time without any problems, but suddenly it stopped working. I had my computer turned off for some days and suddenly, the keyboard was back to normal without any problems. But it lasted only for a couple hours.

I have tried to change keyboard input language, and it seems to change the behavior of the keys; however, it is still not as it is supposed to be.

I have tried reinstalling drivers, but it says that it already has the most up to date drivers installed.

What can I do to find out what's wrong? And what can I do to repair it? Since it seems to not work to simply replace the keyboard, I have really no idea what to do.

I don't have a Windows 7 CD, so I don't know how to downgrade from Windows 10 to Windows 7.

Edit
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When I press SHIFT, my computer will automatically go one line down and highlight, so it seems that it presses the down arrow key while it holds the shift button.

If I press right arrow key, the screen rotates just like if I press ALT GR + RIGHT on a normal computer.

If I press CTRL in a browser window, it zooms out, so it indicates that the minus/hyphen key is being pressed.

I have checked on-screen keyboard, and it seems no keys are actually being pressed, so I don't know why it acts like this.

And as previously mentioned, some of the keys' strange behavior change to another strange behavior if I use another keyboard input language.

Answer: 
Try to install a new language. In my case, for example, the problem didn't get solved until I installed English (United Kingdom) Language although English (United States) was already installed.
maybe its a little late, I started having this issues too. It was a Windows update that was causing this. Uninstalled it and everything back to normal. Hope it helps.