Cursor

When the cursor is stuck at top-left this usually means that the Mouse is not detected during start-up.

If you using a V1 Apple Wireless Mouse make sure the removable batteries are full charged and that the on-off switch on the bottom of the mouse is in the "ON" position.

If you using a V2 Apple Wireless Mouse make sure the built-in non-removable battery is fully charged and the on-off switch on the bottom of the mouse is in the "ON" position, try using a different USB charging cable since the original USB charging cables do break eventually.

If the wireless mouse is fully charged but still the cursor is stuck in the top-left position then the next step is to reset the Bluetooth pairing and to do this you will need to connect a standard USB mouse to the Mac temporarily. After the USB mouse is connected use that to navigate to the Bluetooth icon in Preferences then select the wireless mouse in the Devices list and then click the "x" symbol to remove it.

Switch Off-On the power switch on the bottom of the Wireless Mouse and left/right click with the wireless mouse a few times until the wireless mouse reappears in the Bluetooth devices list then right-mouse click with your USB mouse on that device and select "Connect" to re-establish Bluetooth pairing. Once that is done you can disconnect the USB mouse and return to using the wireless mouse.

If the Apple Bluetooth wireless mouse is not detected and not visible in the Bluetooth devices list then carry out a SMC and NVRAM/PRAM reset on your Mac first and if, after all that, the Apple Bluetooth wireless mouse is still not detected but your Apple wireless keyboard is detected then your Mac Bluetooth module is ok but the wireless mouse may have failed.

How to reset the SMC of your Mac - Apple Support

Reset NVRAM or PRAM on your Mac – Apple Support (UK)

Finally, if you are using a USB wired mouse and the cursor is stuck at top-left then try a different mouse, the mouse USB cable is probably broken.