Hello and welcome to the forum.
My first suggestion would be to run the built-in System File Checker utility, by opening an elevated command prompt
Click the start orb->All Programs->Accessories->Command Prompt (right click and choose run as administrator
Type
sfc /scannow
See if the System File Checker finds and repairs any issues.
Confirm that osk.exe is present in C:\Windows\System32 and see if you can double click and open it from there.
Disable the OSK, (uncheck it), reboot. Go back and re-enable it.
Create another user account (administrators group) and see if you can launch the On Screen Keyboard using that account.
Good luck and keep us posted.
Regards
Randy