My new iMac 24 inch 's blue tooth mouse lost connection with my iMac. How do I re-establish that connection since upon restart the mouse arrow is still parked at the upper left hand corner of the display and does not respond to mouse movement?

• first check the mouse is turned on with the switch next to the optical sensor (up is on)
• charge the mouse for a couple of hours
• if it is on but not working you will need a wired mouse and do as already mentioned

Turn the computer on and plug the cable you got with the computer:

Unfortunately, you can't use the mouse while charging it.

Recharge the built-in battery in your Apple keyboard, mouse, or trackpad - Apple Support

This is when you need to borrow or buy a wired mouse so you can then re-setup your wireless mouse. This is one reason why I have never bothered to use either a wireless mouse or keyboard.

I have a new iMac and while setting it up my mouse is stuck in top left corner of screen?

Is your Mouse on? You might need to follow the steps in this thread.

If turning it on and charging it does not help, you may need a wired mouse.

How do I charge the mouse?