Cold radiator caused by bleeding?

Firstly, check Boiler Presure, increase to Bar or Bar and a half if necessary. Secondly, Thermostatic Valve, could faulty.

Try turning your other radiators off at the valves. If this causes the cold radiator to come on you have a balancing issue.

Bleeding radiators is not a simple task, there is a certain way of doing it. You have now lowered the pressure and must top it up again, but I dont recommend you do this yourself . I advise you call a Plumber and have them do it for you.

There could be a few reasons as to why it may still be blocked. 1. The valve is stuck in the closed position or has become blocked by sludge 2. The pressure on your boiler could be to low if you have a combi boiler then just top the pressure up to just over 1 bar. 3. Or there could be an air lock depending on the system you have if it is gravity. 4. Your system may need a clean as there probably sludge in the bottom of the radiator as to why it doesn't get as hot as the others anyway. But the only thing that could solve all of these at the same time is to have someone come and check everything for yourselves to make sure things can be ruled out and hopefully it will be something simple to sort. But you did do the right thing by bleeding it you haven't done anything wrong.