The most likely causes are it is turned off or full of air.
Turned off - try the on/off valve at the bottom, then take the cap off the lockshield valve at the other end of the rad. Normally they are the same as the on/off end, but with a cap to stop one fiddling with it. Try turning it anticlockwise (but count how many turns you do - this end balances the rad).
Full of air - bleed using the valve at the top of rad using a key. However even if the rad is full of air, you can usually feel a little heat from the pipe ends close to the floor.