Udit you are going to encounter this kinda spikes in your life.
But i am sure you are brave enough and strong enough to tackle this.
Dipdude has summarised his suggestions in a great way so it cant be better than that.
1) Can't Walk
2) Can't Sit
3) Can't Breathe on my own
4) Can't Play PC games properly
5) Don't have a Girl to Love
6) Don't want to trouble parents & friends with the first 5 points thus pretend to be Happy & Lie
for 1) and 2)
But no one can stop from thinking and dreaming, believe in yourself and believe in almighty.
You can do a lot which normal persons dont do even if they can.
Look around net for inspirational stories, believe me there are much more than you can imagine.
ie : Stephen Hawking, Late Christopher Reeve, Hellen Keler, and many more.
for 3)
Take it in your stride and you have ventilator on your bedside for a support so you need not worry about it.
And a friendly advise : Dont exhaust yourself trying to breath yourself let the machine do its work and you do yours.
for 4)
playing games is not the only thing on net there are lot more creative ways to pass off your time.
and you have started one yourslef (writing), second i suggest is take up photoshop create good images and touch up someone else`s images.
and if you cant think of anything then there is always BD, XTO waiting for tp on orkut and gtalk go and bug them
for 5)
this is purely subjective, and love to a girl can be ina lot of way (you can be a loving son of a mother, you can be a lovely brother of a bubbly sister, you can be a friend, you can be a proud father of a budding daughter, you can be a solacing collegue of a work partner and lastly i assume you want to be loverboy of a girlfriend)
out of those much you cant be something, but i am sure you are atleast two of them. go on and do that finely and to your best put smiles on you mom and sis`s faces.
If you have a girlfriend and you go on dates and enjoy life, if that the way of life i dont think its so. thre is much more to life than just a girlfriend.
For you a way out is you can find some good person on internet need not be of your age but definitely a genuine, good friend. You are smart enough to find yourself.
for 6)
If you say you can hide your sorrow from parents then man you are kidding, it is more difficult to keep surviving a disabled child who is understanding and smart enough to face real life.
whatever sad moments you have seen in your life span your parents and family members are seeing daily in their personal life. Eventhough i havenot met you or your family personally but being a doctor i have encountered this kind of difficulty in my career.
I am older than you, and during this life span which i have lived i have learned a few things,
The world is nice place if you are nicer to other people. Believe me really fate always has some pleasant surprises for us.
Joy is in giving rather than taking, especially asked for or demanded love or affection is of no value.
Depression 
can't type much due to sadness the reasons for this are:
