My Big Problem

I've just got a really big problem. Hope you can help me to leave from this problem. In a couple days ago *till now* I cannot leave a comment. It's not blogger's problem but my WordPress (WP) problem. Since couple days ago, I cannot leave a comment for my friends' blog, and I've no idea bout this..I don't know why it is happen? Is there a problem with my WP? Or problem with my computer, or my network? I only can leave a comment for blog where I signed in. So, can anyone there help me to solve this problem? I really feel upset, coz my friends asked me to leave them a comment in their blog.
Plizz...