Server machine problem

We are using SBS 2003 with 10 clients. The system is working from morning 9.00 to night 9.00 clock, while all client are working.

When I come to office next day, the Server system power is on, but no hard disk activity and no display in monitor. This is happening for the past 2 days.

Please help me.

A little more information would be useful here. When you come in the next morning, is the server accessible from the network or not? What do you do to get the system back? Is the server protected by a UPS? Ans has anything (hardware or software) been changed in the last few days?

yes, the server protected by a UPS. Actually in Server the External NIC sometimes show "Local Area unplugged and now it is connected". This will happens 3 or 4 times a day.

I thought might be cable problem, so I have changed the network cable, no use. I have changed the new NIC card Intex RTL 8139 and installed driver given by them (software is for Windows XP and Windows 2000) used Windows XP's driver. (3 weeks before I had done this).

But no use still I got the same problem, So I have opened Server box and checked whether the card inserted properly and changed the slot, still no use. (last week I had done this).

Nothing else I had done. This is happening for the past 2 days. So I will forcely shutdown the Server and then start.

Can you please help me.

Your network card problem may or may not be associated with your other problem.
Let's take the network card issue first. Is your server connected to a switch or a hub? I presume it is. If so, check the port speed and duplex mode of both the port on the switch and the NIC card in the server. You either want both set to 'auto' or both set to the same speed and duplex mode (for example, 100 FULL). If the spped and mode are different at both ends or if one end is Auto while the other is fixed you will have problems.
Second, your server issue. Have you checked the server event logs? Even if they do not identify the cause of the problem they might at leas show you what time it happens. For example, perhaps some backup software starts at the same time each night and crashes the server

I had a problem like that a few years ago, I beat my head for the longest of time, did all the same steps, new NICs, drivers, heck I even put new server boxes in place ensuring I used all new hardware just to find my issue was a goofy HUB, replaced it and I have never had that issue again. In a test network, I did confirm that my issue was indeed the HUB.

No we don't have any backup software and only one Server and all others are client machines only.

I have checked the power options, but no use.

I have enabled Perofrmance report on Server, so I go email that Server was shutdown at 12.30 AM.

But the system power is on, but no hard disk activity, no display in monitor.

Please help me.