Hallo everybody,
Thanks for all the answers. I have contacted HP's chat online and gone through the problem with 3 different technicians. I've tried a lot myself too. The issue was partially solved by restarting the printer spooler, i.e. stop, then start and then restart it.
However after I was so happy that the printer worked, I turn off everything. When I turn on again, it was not working anymore. Then I tried to see by exclusion what the problem is, I had to restart the Hardwar I don't know how many times.
Conclusion:
1. The USB cable must be plugged into the airport express before turning on anything.
2. Turn on the printer first.
3. Turn on the airport express and the computer.
4. If you try to print it doesn't work, even if you reset the airport express through the airport express utility software. The printer is recognized and appears in it though.
5. Disconnect the USB cable from the airport express and connect it to the PC directly.
6. Print a document.
7. Disconnect the cable and reconnect it to the airport express.
8. Now you should be able to print wireless. You may need to reset the airport expresst with the utility softwar, but I managed to print without having to do it.
9. The pörinter works even if you turn off and on again the computer, or you suspend the windows session and restart it, or if you put it in standby and restart it.
10. The printer works even if you turn off the airport express and the computer, or the airport express alone and restart them/it.
11. The printer doens't work anymore if you turn it off and onn again. In such a case you have to plug in/out as discribeb above.
Solution: Leave the printer always on, or make the plug in/out every morning when you start the computer and print one page direclty before being able to print wireless.
Does anybody have a solution to this problem? I mean it prints, but it is annoying to plug in/out every day, no?
HP's technician says that it is not a recommanded solution the HP Laserjet 1020 with the airport express, since the printer works on a host based server basis... I mean it is easy to say that, but one expects to buy a printer that works always and not to have to plug in/out everyday, restart spooler and so on.
Can anybody comment or suggest anything I can do to avoid this? Thank you and I hope this helps others too.