Unable to switch digi box off/change channels with remote?

Matsui Digi box (M1STB09) bought less than 6 mths ago from Currys. Worked well up until a couple hours ago, the green light won't switch off, or let me change the channels, have unplugged everything and plugged bk in again correctly, have changed batteries in the remote and still not working. Channel is stuck on channel 5 and unable to change to other channels, or switch the digi box off!!