Market problem :(

[Sadra1122]

When I open my market app, It stays "Loading..." For a few seconds, then it closes to main screen.
It does not say any error. :'(
I also know that Market is now google play store, But If I download the apk, It says authentication required. Please log in to your google account.
Help please

 

[Sadra1122]

Oops, Sorry I put it in the wrong section.