1801 microcode update Error missing or invalid .processor micro code update please contact hewlett-packard company for new micro code update to support the new processor stepping. I've got is a 2004 model year, the HP dc5000 SFF computer and I switched to the second processor, because the original went failure.Now has started up, the machine will notify the above error.Where fault?What's your problem?

SOURCE: 1801 microcode update Error missing or invalid

This usually happens when a new system pcb is installed in the unit if you go to hp web site and go to support and drivers. Then select download drivers and software then enter the model number then pick OS the BIOS you will be given the Microcode.
Note there are many ways to update easiest is to find the usb boot disk as most pc dont have fdd's any more .