sharepoint 2003 problems

[abbood]

Hi,

First I would like to thank you for this forum which I'm sure it helps lots of ppl.

I'm an admin on sharepoint 2003 portal which suddenly started acting strange !!

1- I lost my admin menu (where I can create a subarea..etc.)
2- users get a pop window to enter user/pass.
3- users & me(admin) can access some links other links says we don't have access any more ?

Note :
* using sharepoint 2003 server
* on portal permissions I'm still admin,users still have read access so nothing changed there ?
* I'm not sure if it's a network/windows 2003 server/sharepoint problem ?

Please help.

Thanks