It's an add-on indeed that is causing the issue. Once I reseted IE7 to the defaults, it placed every add-on into disabled state, Then gmail behaved normally. Then, after many trials I found out that 3 add-ons related to FlashGet (A dowload manager) cause the problem once they are enabled.
I've been using Flashget since like before I was born. Never had an issue like that. I guess I'll have to try the newest version.
Thanks ZiPPy and all.
