Computer Drops off Workgroup?

Hello.

I currently have an older computer that just started acting up but was working fine for years. Basically when I start copying/moving files off its HDD over the workgroup either from that computer or from another computer over the network it will drop from the workgroup and my copying/moving will stop saying it cant find the computer. The thing is the network ICON on that computer doesn't disconnect or anything but I can no longer access the workgroup or get on the internet and have to re-boot the machine.

Would something cause the network (10/100/1000) to over heat and drop out or is it something to do with Windows XP?

I have re-installed the latest networks drivers for the Dlink DGE-530T 10/100/1000 network cards as well as turn of the power savings mode on it as well.

Could this have to do with IP's or anthing?
All my computers have static IP's.

What would cause something like this and how do I fix it?