Your HP Deskjet 3845 printer includes several diagnostic tools to let you know when the device is experiencing a problem. One of those tools is a warning light that flashes on the power button continuously. If you want to stop the blinking light, you need to resolve whichever problem is causing the warning light. A blinking light on the 3845 model indicates either a paper jam or that the paper rollers inside the device are dirty and need to be cleaned.
Unplug the power cable connected to the back of the printer. Grip the bottom edge of the blue plastic cover at the top of the Deskjet 3856. Lift open the cover so the paper feed tray and the ink carriage are visible.
Pull out any paper sitting in the paper feed tray. Check in the back of the printer to see if any paper is jammed in the back of the tray. Grip the edge of the stuck paper and firmly pull it toward you to remove the paper jam.
Turn the printer around so the back plastic door is facing you. Push in the latch at the left end of the door and pull the door off the printer. Check inside the paper rollers to see if there is any jammed paper. Pull out the paper if any is present.
Moisten a cloth with water and wring it out so the cloth is just slightly damp. Wipe off the rollers gently with the cloth to clean off any dust or debris.
Set the plastic door back into position and push it gently toward the printer until it snaps into place. Turn the printer around so the front is facing you. Set your paper back into the paper feed tray and push the grey plastic paper guide up against the left edge of the paper stack.
Close the top plastic lid and plug in the printer's power cable. Tap the "Power" button to turn the printer back on without the blinking light.
The Deskjet's power light will also blink if the top cover is accidentally left open. To stop the blinking, simply close the top cover. The Deskjet 3845 model includes an option to print a self-test report, which lists any problems the printer is currently experiencing. To print a self-test report, press the "Power" button. With the button held down, open and close the cover four times. Release the "Power" button to start printing the report.