I have a designjet 800ps 42" and send me the 79:04 error code, after this happen i change the belt and all the printheads, but it still send me the same error, it said Error Code:79:04 alignstorage.co,644 i try to align the printheads in 11 minutes mode, but it failed every time that i did it, my problem is that the vertical lines print broken lines. how can i fix this?

Who told you to change the belt? 79:04 is a Firmware error.
Switch the Printer Off and wait a few minutes. Switch the Printer On again and check if the Error Code has disappeared. If the Error Code reappears, check for a new Firmware release. If the new Firmware release does not solve the problem, or if new Firmware release was not available, then contact the HP Response Center supplying the following information: - Model and Serial Number of the Printer. - Firmware release of the Printer
- The complete Error Code information, including the linefeed where the error occurred