OK try this -
1/. Unscrew the TRV heads from the valves and use a pair of pliers to try pulling up the little pins since it may be what kev said and that they're jammed.
2/. If no joy, then put the TRVs back on and close all the rads at both ends, including the one that works. Pressurise the system to about 1 1/2 the working pressure. With the heating turned on at the combi bleed each radiator in turn, by turning its valves on at both ends, then closing the rad off again at both ends, but (unusually) leaving the one nearest the boiler until the end. Make sure you top up the pressure as you go, until the last rad. When you've done this, get the system up to normal working pressure and reopen all the valves. Before anyone else laughs, you can see wht I'm trying to achieve here - chasing any airlock out back to the one rad that does emit heat.
The only thing left to possibly bleed will be the boiler itself, and on this I am unsure of what to do and someone else may step in here.