Probably not a blockage - are other radiators hot?
Need to ensure both inlet and outlet valves are open (anticlockwise) and that radiator has no air in it - little bleed valve on top of rad - need a special key with small square socket. Undo bleed screw turn and a half and wait for water to come out - have an old rag handy to catch the water.
Peccavi
November 2008