Suresh, sign in box is opening on my own installation in Spring theme. Most likely you have custom code inserted on your site and it is blocking sign in form from opening.

no allia i havnt used any custom code.. sign in box is shown in my local installation but not in my sit.. i get only that black shadow

Suresh, can I check this on your site? ( need your site URL)

riffbuzz.net

Suresh, I was not able to check this on your site, since currently you are using "Origin" theme.

Edit: i have changed the theme

I am using Spring, but have no such problem.

Try deleting it and uploading it from Oxwall again.

i did that but its also the same..

ill post a reply after turning on off dev mode

Thank you for changing the theme.
I can see "Sign In" box.

it worked after enabling and disabling dev mode

 Glad to hear that everything is ok now.

i cant login and i cant access admin page it shows 404 error

Have you checked the .htacces file?

i have zero knowlege on this what to check in for in the htaccess?

Suresh, please create a separate topic regarding 404 error.

Search the forum for ".htaccess" keyword. There are a lot of topics with solutions out there. Just need to search. ))