Your IP address (169.254.x.x) shows that your PC has not connected to the firewall properly.
Try rebooting your PC after connecting to the firewall. Most 3Com firewalls give the PC an address which looks like 192.168.1.###
Alternatively start a command prompt and type
(then press return)
and wait (can take a while on XP) to see if it comes back with a better address.
Having an address of 169.254.x.x means your PC did not find a DHCP server.
So another possibility is that the firewall DHCP server is turned off. Is this a new firewall (in which case it will be on)?
If not you can reset many 3Com firewalls to default settings by using a network lead to connect the WAN port to one of the LAN ports, booting the firewall, then unplugging the network lead and rebooting the firewall.