LG32LZ55 TV GOING INTO DPM MODE

I have recently connected my computer to my tv through the only DVI socket using the DVI/VGA cable with ease and all works fine but i also have a Virgin HD V+ box which works through a DVI socket also so after a while to keep swapping over the cables got a little tiresome so i bought a 2 way switch - this is where the problem arises i connect a DVI-I to DVI-I cable from TV to switch box and then out of output A i connected a DVI/HDMI adapter with a HDMI cable to my V+ box and then out of output B connect the DVI/VGA cable to the PC - i thought brilliant this will work but no - TV works absolutely fine when in A but when i flick the B switch to go into PC mode the screen goes into DPM MODE - i only know this as a power saving mode but don't know how to rectify it - Please help!!!