Laserjet 1200 printer blinking yellow led continuously what can be the problem

Try resetting it, i.e. remove the USB cable from the computer and then unplug the power for a good 60 seconds. If that doesn't do the trick, it could be indicating that it is out of ink or there is another issue with it. There should be some sort of diagnostic software that came with it in the driver package/software CD if that happens to be the case.

The printer has an error. The door is open, the media is out, the toner cartridge is installed incorrectly, or the paper is jammed.
1. Check that the toner cartridge door is
completely closed.
2. Load media into the correct input tray.
3. Check that the toner cartridge is correctly installed in the printer. (See
“Toner cartridge” on page 78 for more information.)
4. There is a paper jam. (See “Functional checks” on page 149 for more
information.)
5. Check that the door and toner cartridge interlocks are operating
correctly. (See "Paper path check" on page 155 for more information about the
door interlock.

For the Service Manual go to this site. http://image1products.com/techdocs.new/