avast Home Edition were installed In the two computers , one of the computer Automatic Updates can be successful after each boot computers everytime and another computer is not automatically updated each time that must be manually updated, avast on the two computer are all the default settings . Besides, two computers using the same avast serial number and the system is windows xp Simplified Chinese Version. ???
reinstall can tell us more about your problem if the reinstall cant solve the problem than reply back. Or check this ( Start avast-menu-Settings-Update[Basic] ) and see either the database is tick automatic.
Has been re-installed, but the problem still exists, the settings of update is the same on picture.
Which firewall are you using?
Use Windows firewall,Two computers are the same.Is it because use the same Serial Number?
Ok, that rules out the firewall issue. The same regisrtation number shouldn’t matter. It’s tied to an email address not a machine as far as I know. Besides if that where the problem, manual updates would fail also.
Try an search of the forum, using the search button at the top. Use the key words (without the “”) “auto updates fail” This has been a problem before for some and some have found a solution.
Thank you very much for the warm help. 
Welcome to the forum. Please post back if you do or do not find a solution. There are many knowledgable people on this forum.
Do you have any others anti-virus program installed on your computer? Or previous ? 
No any other anti-virus program on my Laptops and fist install avast on the computer.
Well ok give me some times to think about it While the others might help you out from this problem.
Check if the settings are the same on the Update tab of settings and the Connections one.
Do both computers connect the Internet the same way?