Kobo Mini stopped opening epub books

Hi,
I'm new to this forum and not sure if posting on the correct section:chinscratch:
I have a kobo mini. Had no problems using it in past but a month after warranty runs out it starts giving me problems. First it seemed to just freeze up. Finally got it to semi-work again (power button no longer seems to work) but my problem is it no longer seems to open any epub books that I used to download from the library. The books that were pre-loaded onto the kobo open with no problem ie books that were purchased on it (kobo was a gift) but epub format no longer works. I erased library books and tried to re-load/downlad them onto kobo. No problem in transfering books onto kobo but when try to open them it tells me book is finished or goes into "freeze" mode. I can't move forward or backward in the book...just tells me book is completed. It allows me to open pre-loaded purchased books but nothing else. And yes, I was able to open epub books on the devise previously with no problem at all. Really annoyed by this as it seems to stop working just when warranty ran out.
Any help would be greatly appreciated.
thanks