I hate to say it but your system sounds hosed. I would start over.
As far as your internet connection is concerned, can you ping the gateway PC ? If you can, try pinging the DNS server next then try pinging google.com this will tell you how far you are getting. I usually set up the gateway to be the DNS server too. Of course my configuration is backwards from yours. My linux box is the gateway and DNS server for the rest of the systems on my network.
As far as the permissions, graphics, sound and other problems you are having, there are too many to troubleshoot effectively. I would reinstall and work on one problem at a time.