2003 Focus: making horrible noise from engine

At all speeds my 2003 Focus SE SOHC engine with 110k miles on it began making a horrible clacky sounding noise and stalls when I try to idle the motor. The check engine light began blinking. The oil and
coolant both look fine. When I pulled the plugs I noticed that one of them had the ceramic around the bottom of the metal pole had separated from the rest of the ceramic and slid down over the pole, but it didn't look like anything broke loose into the cylinder. I replaced the plugs and wires.
It sounds like all of the valves are banging around, and it happens at all speeds.
The car was in excellent condition inside and out until this problem happened. I'm getting this sick feeling that I finally may have blown my first motor. I am still on my original timing belt.
Does anyone have any ideas on what may have happened?
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Is the engine check light still lit / blinking? Did you check the coil pack was working?
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