Not much information to go on... it could be anything.
Basically, start from one end and work towards the other, eliminating all possibilities.
Is the amp plugged into an a/c outlet and actually powered up?
If you're sure the amp is working, and turned up and not in standbye mode, turn up the volume and see if you can hear the hiss of the amplifier.

If there is a hiss, then the amp is probably working ok, but not getting a signal from the guitar. In that case, check the connections.
Try plugging something else into the amp, like a mic or even a pair of headphones. Keep the volume low and see if you get any sound.

If there's no hiss, then you've eliminated the guitar and cord as being part of the problem and it's probably something to do with the amp itself.
If the settings are all correct, the on light is glowing away, the standby switch is turned to the right position to turn it on... it's plugged in... the power is on in the house... etc etc... and you still can't get any sound at all... like not hiss or crackling when you plug in cords or anything...
then it's probably time to take it back to the store to have it checked.

(of course the final test in my case is to give it a good kick. Nine times out of ten that usually fixes the problem.)