cannot access dashboard on blog.mobikwik.com/wp-admin

I have 2 blogs: mobikwik.wordpress.com and blog.mobikwik.com; first one is fine. But I am unable to login to my wordpress supported self-hosted blog at blog.mobikwik.com since the last 2 weeks. I cant see the dashboard and both /wp-admin.php and /wp-login.php lead to a blank screen. These 2 also keep redirecting to each other after I submit my user/pwd credentials. I have tried firefox, IE, flock browsers and done the clear cache+cookies stuff -> still no go.

I have been posting to blog.mobikwik.com using posterous but I would really like to access my dashboard and make some changes.

My blog supports my ecommerce business https://www.mobikwik.com so not being able to login and make changes to my blog is hampering my unique visitors and business. Please help!