This is exactly what happens to me. I got the card the same time as my new setup so was wondering what the reason was.
Yeah seems odd, as it does everything normally when switched on, the gfx card fan goes 100% for about a second then slows, the drives kick in, the post screen appears and we load.
Only when i put the 5850 in, we get the gfx card going 100% for about a second before slowing down, the drives kick in, then it seems to sorta hold for about 5 seconds or so with the monitor blank and its light flashing (as no display), then the post screen appears and we load.
Then today after the 5 or so second hold, the post screen was like when you havn't got your Tv aerial in and the channels not tuned, but it was all coloured fuzzyness, then it went off and came back for the Starting Windows Screen (so that was fuzzy coloured), then it went off for the Welcome Screen, which appeared fine, and Windows appeared fine, and been fine ever since.
Restarted a couple of times, all fine, no fuzzyness, no hold, switched off and back on a couple of times after a few minutes or so, and again, all fine, no fuzzyness, no hold.
Only get the hold on a switch on from a cold boot, and this morning got the fuzzy screen as well on a cold boot.
Looked like this (obviously without the HBO logo
), and was all red and green.