Computer completly dead? :(

So i woke up this morning and my computer was working perfectly, then i took a nap, woke up again and it was turned off... so i was like wtf lol... i hear a really weird buzzing sound coming from the power plug in in the back. And I tried to turn it on but all i got was a white light that then just dimmed out and died again. I took the power cord out and it stopped buzzing. and then put it back in and the buzzing was gone but now the computer was completly un responsive and the power light didn't even come on period.

I'm really worried as this is my freelance workstation and I had a lot of valuable info on there, has any1 experienced this before? I'm thinking it might just be a fuse in the power box or something but i don't know the hardware side of computers watsoever... any help would be awesome:

Computer =
Mac g4 tower

I don't know anything about Macs but I would say that it's the power supply.