Printer problem have a hp laser jet p1006 printer, say it has a paper jam but no paper is visible

Even a very small piece of paper (A small piece torn off a jammed sheet) can cause the sensor arm to stick in place giving a false paper jam. Double check the entire paper path (what is visible) using a flashlight.
Also, check for broken "flag" sensors. Basically a flag sensor is a small piece of plastic that is pushed out of the way when the paper is traveling through the unit. If one of these flags is broken it may display a paper jam error as well (The flag after paper travels through will drop back into the paper path.) If this is broken it will not trigger the sensor and thus the error condition exists..
Most likely you have a small piece of paper stuck inside the paper path somewhere.
Do not, I repeat do not use any sharp or pointed metal objects to remove any small paper from within the fuser unit, the fuser covers are very delicate and such poking and prodding will likely damage the fuser covers, causing bad print quality or drastically decrease the fuser life (a small tear will quickly render the fuser useless).
Hope this helps!