We discovered a box on the wall whilst decorating which was once a light switch we assumed. As we no longer needed it (could see where door to outside used to be so thought maybe outside light!) we taped ends of the wires and cemented in the hole to make smooth for wallpapering (did this once before on another outside light and it was fine). Few days later went to turn on the main ceiling light - rather than table lamps - from the dimmer switch by entrance to room and found it not working. It's not the bulb as we tried that so can only assume this used to be a two way switched light and we've messed up. The wires were wired into a junction box but can't remember how. Can we take the light down and adjust the wiring in the ceiling rather than have to knock out the rock hard cement to get to the wires (also now cut v. short by over zealous hubby)? Haven't yet checked what wiring is in the dimmer switch. Any help appreciated - just to make clear (if not already obvious!) - we know very little about electrics!
I assume the wires were in a connector block behind a blanking plate?
Why did you remove the connector block? If you were going to fill the box in then what was the point?
Anyway - thank heavens you did, because it meant you did something that messed up the switching and posted here - if you hadn't then you wouldn't have got to find out that leaving the live wires concealed in the wall like that is dangerous and illegal.
You need to lift the floorboards upstairs and reconnect the wiring to that light so that it only goes to the one switch. Nobody can say without looking what this will entail, as it depends on how the 2-way switching was done, and whether the remaining switch has the drop cable and 2-way strappers or just the strappers. Once you've done this properly it will work, and you'll have disconnected the live wires you left buried with no clue to their presence.
But it's no good trying to do any of this knowing very little about electrics - you need to learn how lighting circuits are wired. See the articles in the For Reference topic and the Wiki, and maybe get a home electrics/DIY manual.
Well it was worth a try! - No can do on the 'lifting the floorboards upstairs' - bathroom heated floor with tiles. I think we'll just have to knock out the cement and a bit of the plaster wall above to expose more of the wire and then call the electrician. Thanks anyway.
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We discovered a box on the wall whilst decorating which was once a light switch we assumed. As we no longer needed it (could see where door to outside used to be so thought maybe outside light!) we taped ends of the wires and cemented in the hole to make smooth for wallpapering (did this once before on another outside light and it was fine). Few days later went to turn on the main ceiling light - rather than table lamps - from the dimmer switch by entrance to room and found it not working. It's not the bulb as we tried that so can only assume this used to be a two way switched light and we've messed up. The wires were wired into a junction box but can't remember how. Can we take the light down and adjust the wiring in the ceiling rather than have to knock out the rock hard cement to get to the wires (also now cut v. short by over zealous hubby)? Haven't yet checked what wiring is in the dimmer switch. 
Any help appreciated - just to make clear (if not already obvious!) - we know very little about electrics!
