Remote problem on Grundig WF70-3020?

I have the above Tv which hasn't been used for a few months but was fine last time it was used. Recently I switched it back on at the set (it had been unplugged) and it went straight to the co ax aerial connection. We have a freeview box on this which works fine but the remote would not let me switch to the AV channel, or in fact anyhting at all, including standby. I have changed the batteries several time, but still nothing. So I now have an all in one from Woolworths (not a cheap one) but none of the grundig codes work either. I can put 991 and try switching off until I find a code that works but this may take a long time. What I would like to know is how do I find out if it is the original handset that is broken or the infra red on the TV?
Any help would be appreciated otherwise I will have to buy a new TV. I don't think I can change channels on the TV itself.