Thank you Tumblr team!
My access to Tumblr has been restored. :)
For some reason I was being blocked late this afternoon and evening. I was able to access the site via a proxy (hidemyass.com), but not directly. I emailed the Tumblr support team, if my IP was being blocked, and if they are the once who restored the access, then “Thank you guys for the quick work. And thanks for being up late looking through emails.”.