C:\Windows\ERDNT <-- This message is caused by ERUNT wanting to make a registry backup but ERUNT may be damaged, open it up and disable any automatic backups, really dont need it now.
As far as FF freezing when you plug in your lan cable, not sure, have you turned the computer off, then plug in your cable and restart yourcomputer and see if that helps.
In your original post you stated that things ran fine in Safemode but a lot of things where unresponsive in normal windows, you may want to think about doing a System Repair and maybe even a format of your hard drive and a fresh clean install of windows, if you want to do this let me know and I can link you to a windows forum that we work closely with that can help you. Do you have your windows CD or the Recovery CD that came with your computer ?