Here is the most important thing to understand about paper jams in any printer....
The printer does not know if there is a paper jam anywhere in the printer.
What it does do, is respond to sensors ( optical sensors, either open or closed, by plastic flags). These flags are moved as paper moves through the paper path.
One example of a paper jam message when there is really no paper jam, is when the feed rollers are worn and do not pick up paper from the paper tray.
When you start printing
, the printer expects that first sensor to open ( paper passes the sensor ) at a very specific point in time. If the paper did not get picked up from the tray, then the printer will ASSUME that the paper must be jammed somewhere because it did not reach it on time.
Now this will also happen if in fact the paper did get picked up and then jams prior to the sensor.
So... if you get the picture of how this works, understand then too, that if the printer is showing a paper jam message at power on, then one of the flags is open when it should be closed.
If you do not actually have a piece of paper holding this flag in the open position, then the flag is possible broken.
I usually see this kind of damage occur after a true paper jam, where the paper is removed either in the wrong direction ( pulled out back the way it was going instead of the way it should normally travel ), and this breaks the flag, or it was pulled out forcefully again, catching on and damaging the flag.
All of the above pertains to ANY printer, and not just yours. you must take care to fully inspect every inch of the paper path, from the paper tray, to the exit, use a flashlight, and look for the sensors and make sure they are not blocked or broken.