Q: how do i fix mac mini cursor stuck in upper left hand corner

Try disconnecting then reconnecting the mouse. If that doesn't help then shutdown the computer and restart.

What happens with your mouse if you boot into your Recovery HD?

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

Sounds to me as if you either have a bad mouse, or you could have your mouse on an unsuitable surface. Try placing the mouse on a different surface, a commercial mouse pad, the leg of your blue jeans, etc. and see if the mouse works properly. Whether that works or not, I would recommend thoroughly cleaning your mouse following Apple's instructions here. Apple does not recommend this, but I have had good luck cleaning a mouse by using  an alcohol pad or a household cleaning wipe. Just be sure to let it dry thoroughly before plugging it in or re-inserting the batteries.

If you leave the system running for 10 minutes does the mouse begin working again?

My wife's Apple iMac 2013 has the same symptoms; on reboot mouse freezes in the upper left corner of the screen for approximately 6 mins then something timesout and it unfreezes.  This is becoming quite annoying as you might imagine.  Have tried some troubleshooting actions but nothing has fixed it so far.  Has been this way for a month and predates update v10.8.3.   Any suggestions are welcome.  Apple Care didn't have any other than return the system to our local Apple Store for 4+ days.  With financial documents and other data we do not consider that a very vialble option and are thinking of returning the entire system, since other users with these symptoms report even a complete OS reinstall does not clear the issue.

With moderately rusty *nix/Linux skills I am fairly comfortable with the terminal window.

Hi, I just had the same problem a few minutes ago. I installed some software to hook up my PS3 controller and configure it to use with my Mac and after around 10 minutes of using it my cursor just shifted to the top-left of the screen and didn't want to move! I got into Acitivty Monitor using the keyboard and managed to stop the processes of the program I had installed and then restarted and everything was back to normal.

I know this is simple but it worked for me and might work for you.

Is your wireless mouse (Bluetooth) paired with another Apple device like another Mac or iPad?

You say this is a wireless mouse. First thing to do is to check the batteries.

Next click the mouse a few times. If that does not do it, get yourself a wired mouse to investigate why the computer is not seeing the mouse.

Please also tell us more about the mouse - is it a bluetooth mouse, or does it use a dongle, or,...?