when i try to connect to another pc from network places using network cable i get box appeared "user name and password" required ,and the same when he try to !!!but i didnt set password beforeso what can i do???

Open Network and Sharing Center and click the Change advanced sharing settings in the blue area to the left. Click the down arrow adjacent to Home or Work. Towards the bottom in the Password protected sharing area, select Turn off password protected sharing.

Also note that you need to create same user on both computers. If the issue persists, change the authentication level to Send LM & NTLM responses or Send LM & NTLM - use NTLMv2 session security if negotiated in Windows 7 beta. Network security LAN Manager authentication level Security Configuration EditorArthur Xie - MSFT