Hi UKJoshi,
Sorry to hear about your problems but hopefully a reset will solve your problem.
I had a similar situation with my 600 a while ago and I fixed it by pressing the reset button on the bottom of the device. I'm not sure where this is located on the 505, but I would think in a similar position.
If that does not fix it you could try a hard reset the instructions on how to do this can be found here -
https://wiki.mobileread.com/wiki/Sony...der#Hard_Reset
Good luck.