I noticed IE 8 doing something similar on one of our network computers the other day. Try going into your control panel, clicking on network connections. Then right click local area connection. In the next menu, scroll down to TCP/IP and right click it. Go to properties and make sure that obtain an IP address automatically is checked. For some screwy reason when I installed IE 8 on a computer, it went and changed these settings, thus the inability to connect through any browser whatsoever even though the network was still functioning.
Hope this helps!