raspberry canes sick

I planted 18 canes about 6 yrs ago (3 varieties) Last year had a mammoth crop and masses of new canes.  These all appear to be dying now. Some canes have never come into leaf, others have dying leaves and a very few small fruit which are dropping off.  There  are also very few new canes appearing.   Am I going to have to get rid and start again.   Also have a loganberry at the end of the rows - this seems OK at present but is it likely to be affected?   Have seen some problems which suggest replanting in new site - not so easy  and would involve digging up and transplanting the loganberry.   Due to the large amount of rain we had last winter the canes spent a lot of time under water, could this be the cause and might they recover eventually.  Grateful for any advice.