Suchitra Kumar :
I'm in a confusion as which is the brand which durable and gives long life. Which brand among DELL , LENOVO a ACER would be the best and meet the above criteria.
That's a tough question. Most vendors have good laptops and bad ones, There really isn't a laptop superhero brand. You need to nail down exactly what you want from your PC. In other words, it comes down to the specific model to determine if its durable, reliable, long life, etc.
Is this a desktop replacement? Do you want something that is highly portable? What are the uses of the system from most important to least? How much battery life is important to you?
Here's a place to start:
www.pcworld.com
They review a lot of notebooks and have them categorized according to budget, use, etc.
Regarding the brands you mentioned, Dell provides good customer support, and offers good warranties, however you will pay for them especially if interested in a 3 year warranty ($200+). The best thing about Dell is that their laptops are highly configurable, I don't think anyone offers the options that they do.
Acer makes quality netbooks, although I don't know that I've ever really seen a very durable netbook. Lenovo is known for their business machines, but usually are pretty plain jane in their appearance.
If interested in Gaming, I think you have to give alienware a look. www.alienware.com