Try THIS:
Option #1:
1) Open "Device Manager" (Control Panel...)
2) Find "Keyboard" section
3) Right-click and "Uninstall" everything under "Keyboard"
4) Right-click almost anywhere and "Scan for Hardware Changes"
Option #2:
1) Turn Windows OFF (not Hibernate or Standby)
2) Remove keyboard
3) *Boot into Windows
4) Turn OFF PC again
5) re-attach and boot to Windows
*You might not be able to boot if your keyboard isn't attached. There's a setting in the BIOS to ignore that.
Option #3:
Try a different keyboard.