well now I tried to boot with my discrete card and nothing shows up and after few seconds the pc automatically switches to integrated graphics , is something wrong with my GPU or it has to do with the PSU
The only way your going to be able to tell is testing the GPU in another machine. No one will have a tell tale way of knowing for sure if the card is dead. It can be the PSU no longer has enough umph to push the card and bombs out and resorts to integrated.
BUT, I would stop trying to boot about 30 boots ago. There is a huge possibility when it comes to failing psu's that you could be ruining components.