Domain Logon to NT4.0 Server takes multiple tries...

I've got a network of about 15 computers. Most are running Windows
98SE. There's a couple of Windows XP Pro machines, and the Server is
SBS 4.5 (NT4.0).
Had some power issues recently, and now have login problems all the
time. Typically, the first person logging on in the morning has no
problems. After that, it usually takes 3-5 logon attempts for others
to get onto the domain. During this time, the user is told that their
password might not be correct. Each time, they are just clicking OK
again (Win98 stores the password in the domain logon field), and
eventually are able to get in. This tells me that they've got their
passwords entered correctly...
Any help would be appreciated...

-Tim