can't connect to shared network folder

Hi,all

I have a problem in connecting network folder in file server.
Everyday, when I turn on the PC, usually I can access the folders and
files in file server without problem. However, sometimes, I can't
access file server. (it said the file server can't be connected), but
I am sure my connection and the server is alright because I can browse
internet and ping the network server and my colleague can access that
server. Sometimes, it just ask me to login again. However, I already
login the domain already and the file server is in the same domain.
I am using WinXP Pro and the file server is win2k

Any suggestions?

Thank you in advance.

Regards,
Alister