What to do when Windows thinks you are holding the Shift key all the time?

How to fix the issue of Windows acting as if the Shift key is always pressed?


I have a Lenovo Ideapad S410p laptop running Windows 7 64-bit. Recently, I noticed that some of the keys on my built-in keyboard are typing in uppercase even when the Caps Lock is off. This affects all keys and shortcuts except for ZXCVM, which work normally. The problem persists even when I use an external keyboard, but then ZXCVM also type in uppercase. I cannot type any numbers either.


I tried to solve the problem by disabling the built-in keyboard driver and installing an incompatible one. This stopped the unwanted behavior, but it also disabled the touchpad. I can use a USB mouse instead, but I would like to know the root cause of the issue and how to fix it properly. Any suggestions from experts are welcome.