I now believe that this is simply a hardware problem.  The ethernet connection is connected directly to the motherboard.  I suspect something there no longer works since the error of  no #C90X NIC is obtained when diagnosing the system BIOS.  Fortunately, I had a spare wireless adapter handy and had no problem connecting to my wireless router that way.  My computer is almost 8 years old.  Failures are to be expected.  I have also recently purchased a USB - ethernet converter which I have not yet tried but suspect it will work as well since the wireless connect worked.
I have a retiring Dell Dimension 8300 which I will be retiring but want to keep running.  I have just replaced the hard drive that failed but now find I cannot connect to my router using an ethernet cable.  Device Manager tells me I don't have the proper drivers, but I know I do and my computer does not recognize it as a proper driver for my ethernet connection, but it does indicate an ethernet connection present.  The back light for the ethernet connection is lit.  When I run my 2con Nic Configuration Utility/Diagnostics, I get the message: No 3C90X NICs are installed on this computer.Anyone have any ideas on what might be going on?  I had no problem connecting to the internet before this.  Any advice?
3C90X NIC has disappeared.