Mr bubbles, I think I've figured it out.
Seems as though powerplay is messing with your system. It is quite common amongst Ati cards because it seems as though windows doesn't like the video card to be switching clockspeeds during apps. I remember hearing about this in the summer or 08 when i first got my 4870 512 but it didn't affect me, and slipped my mind.
There are a few ways to remedy this.
You can make a custom bios(back up your old one first) that eliminates the 2d clock mode.
Or go to this link
http://forums.amd.com/game/messageview.cfm?catid=260&threadid=100048&enterthread=y for a useful thread
I stole this qoute from the thread
"In Windows 7 Windows Media Player is always active, a quick check in the task manager will show it running as wmplayer.exe. If your card is not clocking up to the correct speeds you can kill this process and the speeds will reset to normal.
The AMD GPU Clock tool will allow you to see what the UVD status is, if it's flagged as "BUSY" your card will be locked lower. The issue at hand is that, if you exit Windows Media Player, it doesn't truly exit it stays active and hidden, it also doesn't release the UVD status.
If you override the clock speeds of in my case the 5870, to hold at stock speeds 850/1200, and run WMP to play a UVD supported video this will stick the system in a crashing loop until you alt+f4 the playback screen.
It seems that the UVD chip simply cannot handle the higher clocks speeds of the 3D processor. One thing that AMD/ATI should have considered in this release is that some of us actually multitask while using our computers. Personally I keep windows open on different monitors with different things happening on each.
I've investigated this with my other system running 4870's and Windows 7, if you play a video that triggers UVD it moves the clocks up to 750/900 and sticks them there, much higher than the 5870's. It also doesn't release them once the video is closed, unless again, you end process on WMP.
The problem here is two fold, the UVD processing units (2.2) included on the 5870's cause the 3D clock to not run at full speed, and secondly, Windows Media Player doesn't release the UVD status. Anyone can verify this for themselves using the tools mentioned. I am very concerned that at this point I might not be able to run dual applications on this card, say watching a movie on one monitor, and having a game on the other without the clocks being turned down. Currently this is the case.
People running the Logitech Game Panel Software version 3.03 are seeing this issue a lot more prominantly, 3.03 activates the WMP extentions for Sideshow, this locks UVD as active until the Wmplayer.exe is forced to close."