My computer will not start it is showing flashing between a mouse and a drive and showing support.apple.com/macsetup

The Mac is searching for your wireless mouse and keyboard.

Cycle the power switches on your mouse and keyboard to see if they will connect.

Or if they are the latest rechargeable models, connect them to the iMac with their charging cable.

den.thed wrote:

The Mac is searching for your wireless mouse and keyboard.

Cycle the power switches on your mouse and keyboard to see if they will connect.

Or if they are the latest rechargeable models, connect them to the iMac with their charging cable.

Seconded. Or, if you have a wired keyboard and mouse, those will also work for now.