When i click buy button items are adding into the cart.But When I do checkout, after logging from account and then filling shipping details,the cart becomes empty.Normally the URL which is followed for checkout is www.mysite.com/checkout/onepage/ but as my cart is getting empty the URL redirects to www.mysite.com/checkout/cart/.I am working on php5, magento 1.7 and nginx as local host.I am clueless about what is happening here. I am newbie.
This question is not answerable for us, because it is too localized.
Some things about cart and login:
When you login, magento loads your account's quote. Then these two quotes are merged. This happens here
The other thing which might be interesting for you is, that the session id is renewed after login. This happens here
Something happens, that either the quote is lost, the products or the session after login.