Depending on when you bought it you should be able to return it and get a full refund, generally within the first few weeks but I don't know exactly - my own computer is the first one I've ever built and nothing was wrong with it. My problems with it I guess you could say are me overspending on parts ($70 bluray drive, $200 on storage, $150 power supply which I could go a little cheaper on etc) now that I think about it. Too late for it anyways seeing as I've bought everything at once in February. I'm going off-topic.
Many poor quality power supplies have died in as quickly as a few hours or days. If I was you I'd try to find any way to get a different power supply. Don't fall in the trap of titles like "Extreme" and "Gaming", good quality computer parts don't tend to have those specific titles as they don't need them.