I am using Corsair VX450 which is one week old. There are no power sucking devices , just one optical drive and one hard drive. No overclocking. I think the issue could be with the gfx card, i do not have another machine where I can test the card.
That is a relatively weak PSU for a HD5850. While spec-wise, it may meet the minimum requirements, it may not be producing its rated capacity under load (like when gaming). If it were me, I would look at improving my PSU, regardless, for long term stability.