Is it normal to block dramatic events from your memory?

Karen
When I was about nine years old, 
My uncle molested me, I stood there like stone, making no sound and saying no words. I hated my self after he'd touch me because I wasn't able to do anything, I was so scared. 
I lived with the pain, and seeing him in my house for years in silence. 
When I turned 15 years old I told my family, and no one believed me... They said how is that it took you so long ? And why did you let it happen....... To be honest I tried and tried to erase from my mind and I'd even tell my self over and over that it was a dream. 
Now here is something that I have in my mind too.
My brother use to make me watch him jack off and watch him shower and I even remember him trying to put his....into me.... Now these are things I've always told my self where all a nightmare but they are real.