Why is my new computer so slow?

I just recently got a new computer. Its the Pink Dell Inspiron computer. I updated it, added Norton Security, i have the sims 3 games on it, minecraft, and little desktop add-ons. But before i even had the sims or minecraft on it, it still was the same. When it starts up it takes about 20 minutes for it to actually be accessible (to where i can actually click on something) and it takes about 20 more minutes for my browser to pop up. i have to click out of it and be paitent and i am running out of my patience. sometimes my whole computer background doesnt respond (Windows Explorer as well) . The task manager doesnt respond quick like my siblings computer when my computer is in fact supposed to be faster than his. It says my CPU usage is high when i go on internet explorer or firefox etc. ... I just got it 2 months ago. But its acting like its 100000 years old. help?