computer acct missing in primary domain

The OS is NT workstation 4.0. The problem is that when the user tries to log on, she gets the message that the computer account is mising in primary domain. Each time, I have to join the user back to the domain and she is able to log on to the domain but the next morning when she reboots her pc, it comes up with the same message again. This has happened about four times and the last time I used the netdom command in DOS prompt. Again, she was able to log on the domain but come the next day aferrebooting, I get the same message again. What else can I try?