Printer blocked on message damaged cartridges and printhead blocked on

Product: Officejet Pro 8620

Operating System: Microsoft Windows 7 (64-Bit)

When I start the printer (Officejet Pro 8620) I get the message "One our more cartridges appear to be damaged. Remove them and replace with new cartridges". When I open the frontdoor for replacement of the cartridges I get the message "The cover or door must be closed to print. Check that it is completely closed". The print head with cartridges does not move to the left and replacement of the cartridges is not possible. The Wifi blue lite is flashing.

Last firmware is installed.

What I have done without success :

• try to enter the set-up menu : impossible

• Hard reset by de-connecting the power supply : no effect

• try to move the print head with the hand : not possible

• use the HP print and scan doctor : can connect to printer with USB to computer but scan doctor gives the following message "printer error" under status...... and the advice to reset the printer.

• I removed the Cmos battery (and replaced it back) thinking that this will reset the software, but with no effect - same messages after start-up.

What else can I do in order to reach the cartridges and replace them ? Dismantle the printer in order to reach the printhead and cartridges ?

Thanks for your reactions.