Extending the RAM memory from 3 GB(3 slots with 1 GB of RAM slots) to 4GB of RAM, by adding a compatible RAM module to the remaining slot(1GB of DIMM 6400 RAM, at 800 Mhz) turned out to disable the Ethernet card. So I tried resinstalling the ethernet driver, the BIOS and motherboard device drivers to no avail.
Ultimately I installed a new PCI Ethernet card and the networks started working. Thankfully I had an Ethernet card stored in a warehouse, otherwise I would be left spending for a new Ethernet card or not possessing network connection at all.
