Network disconnects when the machine is idle

I get disconnected from the network (i.e., the internet) when my machine has been idles for a couple of hours. I need to restart to get re-connected. After three calls into my software consulation company, they were not able to fix it. I am connected with an ethernet cable and there is no problem with the internet service (my other computer works fine). The power management options include 1) allow the computer to turn off this device to save power, 2) allow this device to wake the computer, and 3) only allow managment stations to wake the computer. I unchecked the first one, but it did not fix the problem. If #2 is checked, then #3 is automatically checked (that is, I cannot have #2 as the only option that is checked). Please help! This is a real pain and I have already spent countless hours trying to fix it.

I think that you have selected the option for power saving from the Network Card and this is the reason that when you put the computer idle for some time then that get disconnected from the network. For this, you must check for the TCP/IP properties.

Thank you for the reply. There are three boxes under the power saver tab:
1) allow the computer to turn off this device to save power,
2) allow this device to wake the computer, and
3) only allow managment stations to wake the computer.

I unchecked the first one, but it did not fix the problem. The computer will not allow me to uncheck the third one without also unchecking the second one.

Any additional thoughts?

Which operating system have you installed in your pc? If it is vista then in the elevated command prompt, type in bold below and press Enter.
NOTE: Replace XX with a value of -1 to 65535 minutes. For 30 minutes, you would type:
net config server /autodisconnect:30
WARNING: -1 is to never autodisconnect, and 0 (number zero) will cause an almost instant autodisconnect.
net config server /autodisconnect:XX
After that close it and then try to restart your pc and check if the problem has faded away.