Standalone 2000 server drops connection

I have an older P200, 128mb, 8gb ide h.d. with Windows 2000 standalone it includes a 80gb h.d using a Promise DMA-100 card. This computer has a problem when I try to copy large amounts of data to it. When I try to download data that will take more then 20 minutes it disconnects from the network and I have to re-boot it. I’ve tryed flashing the bios, swapping out the NIC. Both h.d.’s are ntfs and seem to be working fine. It’s ip is setup to use my DCHP. I tried reserving and releasing the IP. Any suggestions would be appriciated.