If you have an Apple Store nearby you can make a Genius appointment and have them check the device over. The appointment and checkup are free. Repairs if required, not so much.
I have tried the reset you suggest but unfortunately as soon as I unplug the mains cable the power cuts off. When I put the cable back in it reboots with the apple logo
I think a visit to the store is my next move.
Thanks for your help anyway