Bicycle Tutor

Hi. I have a Hero Ranger DTB bicycle and it's been a little over an year since I got it. I use it frequently but just recently, I've started having this problem.
When I start riding, I start to feel as if I have to put more pressure to make the handle turn. Slowly as I pick up speed, this seems more evident. When I go quite fast, in say 5th gear (rear), the handle just freezes up. And when I turn it with an effort, it shoots to the direction of the turn, in a very jerky manner.
Earlier, if I used to ride without having my hands on the handlebars, the bicycle would go just fine, and it won't go off-balance. But whenever I try that now, the handle just freezes up straight and doesn't automatically turn in the direction of my weight. This is just an observation which I thought might be worth writing.
How do I free up the handle? How do I make it as free and normal like it was before?
My bicycle: http://www.herocycles.com/rangerdtb1.htm
If you need a few close-up pics of my bike's handle or anything, plz let me know, and I'll respond as soon as possible.

It sounds like a problem in your headset. If this happened suddenly and nothing else has changed, it may be that you have a bad bearing. If you did any adjustments on the front end lately, you may have just overtightened the headset.
You canlook at: http://bicycletutor.com/overhaul-threaded-headset/ for an overview of how to overhaul and adjust the headset.

Thanx for the response. I had asked my brother about the problem earlier, and he too had asked me to check the ball bearings, and oil them. I haven't done any adjustments to my bike, but I will check out the vid you linked for more info. And I'll also check up the headset's ball bearings asap.
Will update tomorrow. Thanx.