Server 2k3 loses connection daily

I have inherited a mess. I am stepping in as IT manager for a small architecture firm in addition to being hired as CAD manager.

Everyday around 4:00 pm, my clients lose connection with the server. This happens whether they are on the domain or on a workgroup. It causes the clients to hang. Can anyone point me in a direction to look?

Also, I have password issues, but after reading posts here, I will not ask anyone to help me hack them. I’ll figure it out myself.