If you have a 3C905C and are trying to use it under Win2K, the NIC is very, very fussy about the driver and being in the right PCI slot. There is a link to a driver that works on the 2K compatability page. If you have another problem in another OS, sorry. BTW, I'd put Intel NICS first, then 3Com, then Linksys, finally Netgear and DLink.