Have I blown my PSU totally?
It may be possible, a capacitor or something
Is there an fuse inside the PSU itself that might have blown??
It's possible but I doubt it, anyway almost all those fuse are glued on the boards, it's more like use and trash stuff. And it may be dangerous to play with it if you dont know what you're doing.
Could I have damaged my other hardware??
It can happen, test with another PSU to make sure
Help!
Some PSU I've used, have a kind of reset when a part blow like that, try to unpluged and turn off the PSU then put it back on, it could work
I dont see what could have gone wrong after I replaced the 5A mains fuse..
It may not be the fuse, but the led without the resistor