Tumblr Problem Please need some help?

i'm encountering so much troubles on my tumblr account everytime i log in on tumblr.com it directs me to www.realgiftbaskets.com but still the URL bar is tumblr.com. i've changed my browser and i refomat my laptop but still encountering the same problem. I can't enjoy my tumblr for about a week, i don't think this is a serious problem hope tumblr finds time to fix technicality. Is there anyone out here experiencing the same problem or anyone knows how to fix this? I need your help badly please :(