Lagging and Overheat

I bought a Dell Inspiron 14z about 5 months ago. Just 4 weeks back, it started to slow down rapidly and got laggy, eventually it wouldn't move at all. So I had to click on the start button to shut it down. When I restarted it, it would work for just a few minutes and then it starts slowing down, until it stops, it just stops. And I had to press the start button again to shut it down. I don't know what's happening. So I got someone to reformat it.

After reformatting, it worked just fine. Then, the problem came again a week back. This time, I notice that the laptop overheated very quickly in just a few minutes. 

Somebody please tel me what to do? Could it be hardware problem that caused the software problem? Gosh. I'm so frustrated. It's so new and I just really can't believe a problem rose from a Dell. I previously used a Dell and it's still working, that Dell was modeled 1525, it's still working after 5 years. 

What is wrong with my current Dell 14z? Should send it in for warranty?