This is from the category of "Not my strongest suit"
From your message, it sounds like the valve at the radiator didn't shut all the way. I have to assume that this is an older system, the type with the cast iron radiators? Sometimes thost valves get so clogged that they don't work properly.
How's your health insurance with Hernias?...... Even when empty, these things wheigh a ton. Get a dolly to move this thing and understand that there will still be some water in it when you disconnect it.
Go to your basement and locate the shut-off valve that should be located between the boiler and the pipes that supply the hot water to your radiators. Close this valve as well as the shut off the valve at the radiator itself. Then try draining the radiator and see if that helps.