Hi P-a-t
I understand you have flashing lights and the printer won't turn on or off.
I would do a power reset to see if that will resolve the issue. With the printer still turned on, disconnect the power cable from the back of the printer, if the printer has external power module with a detachable power cord disconnect it for 15 seconds and then reconnect it. Then disconnect the power cable from the wall outlet. Wait 10 seconds and reconnect the power cable back to the wall outlet first, then the back of the printer and power it on again.
Make sure the printer is connected directly to wall outlet. (don't use a power hub or a surge protector)
Please provide the following information so I can assist you better.
What operating system are you using?
Here is a document to check your operating system for Windows.
Here is a document to check your operating system for Mac.
Please provide the full name and product number of your printer.
Click Here.
How is the printer connected? (USB/ethernet/wireless)