Erm sorry, but the 5850 consumes 151 watts at full load at stock speeds.
The 5830 should be a bit less
I should've noted "when overclocked 200MHz+"
My PC's pulling 480w from the wall with an underclocked & down-volted 3-core AMD CPU running @ 66%, with no peripherals, one SSD, and just one stick of RAM, which I take to mean almost the entire power draw is coming from the two 5850s I have in there.
Still, OCing that little bit may have pushed his PSU over the edge.
Some power supplies have very significant output degradation with heat increase. Simply cooling the PSU better may correct the problem the OP is having. It's a very common problem in laptops, and not impossible in desktops. The intake fan/vent gets clogged up, heat builds up, and output deteriorates. Many owners of gaming laptops find their laptop starts giving BSoDs after a year or few of ownership when it worked perfectly fine originally, and it turns out just giving it a good cleaning fixes it. If it is that problem, it could also be from the days getting hotter depending on where he lives.