Did you enabled Jumbo frames? I did, Now i cant access admin page either.
I have a 1GBit Dell Powerconnect 2716 switch with Jumbo frame support and it is enabled on the switch.
My Ethernet card is Onboard Realtek PCIe GBE Family Controller, Tried with different frame sizes but still no go.
The only computer that could access admin page after jumbo frame enabled on DNS-323 is my laptop with wireless N connection.
Check if you enabled jumbo frame on DNS-323 and did the same mistake as me.
//Zappa666