Network authentication problems

Hello,
recently the office that I work in has purchased a machine with windows 8.1 and I am having difficulties connecting to a server that is on our LAN. All PC's on my network has joined the same workgroup, there is no domain in the network, all machines still can access the server (win xp and 7). There is no other computer in the network running win 8.1. The server that I am trying to connect to is running on windows server 2000. Every time I try to access the server it asks me for my log in name and password as windows 7 did, but there is no password set to any user that can connect to server. Windows 7 worked fine with this system, I just entered the user name and press ok and got connected to the server while the 8.1 once again opens the same dialog form but with a message telling that the log in or password is wrong. I have tier loads of possible working users, I have created a new one and set a password for it and still the same. The interesting part is that I am able to connect to this server from the machine with 8.1 via Remote Desktop...