Thanks everyone!!
But I waited for your reply and disappointed with no reply for 3 days. So I went ahead to cycle using tetrasafe bottled bacteria.
Since there is no way fishes are going to die because of cycle issues in just 4-5 hours, I wanted to figure out the problem. It was good that I waited over 6 weeks without changing the water. I found that my gravel (red and black) were giving away into the water even after having thoroughly washing them and having had them for over a month earlier in the tank....it was the red one especially. My calcium deposits on top of the tank was tinted red and when i was discarding the water, I found that the water also had a mild red tinge to it.
I wanted to confirm if this was what that was killing the fishes and also not allowing any bacteria to build up. So I went ahead and cleaned the tank and sundried my deco and filled the tank without adding the gravel. I bought tetrasafe and a male betta the next day after letting the water sit for an hour. I got the betta in and also added more plants and a driftwood.
THE BETTA IS NOW alive in my tank and seems all happy
so far after over 2 days. I will check the water tomorrow on day 3.
So the problem all along was the grave(l) I bought at the LFS.