troubleshooting a new dish



My Satellite Setup
120cm kuband dish
zenega(dish tv ) receiver
tatasky setup
My Location
jammu India
I just joined the club yesterday. recently i shifted from delhi to jammu. in delhi i used a 90cm ku band dish and watched channels of abs 1 at 75e. as i was shifting to jammu i bought a new 120 cm kuband dish, but when i installed the 120cm dish at jammu it does not even catch the dd channels from dd direct. i have a doubt about the lnb arm which i think is not proper to adjust the lnb at the right focal length. please help me to install the dish and if there is any calculation for finding the focal length. the dish is a fiberglass one.