HD5850 Cold bug?

Me again with yet another problem with a watercooled HD5850....

So for about 2-3 months I'd been getting a "No Signal" message randomly, happened a few times before windows loaded, a few times when just browsing the web and also whilst gaming, It happened about 2-3 Times a week so it was annoying but didn't stop me using my PC.
A few days ago my HD5850 lost signal and so I did what I've always had to do which is to power off the PC and turn it back on again, but this time it kept losing signal before getting into windows, I thought either Windows or the ATI driver may be corrupt so I re-installed Windows... Now I was getting into windows but there were loads of green artifacts everywhere and windows aero wasn't working, At this point I thought the card had died on me.
I thought I'd try reinstalling the orginal cooler and seeing if it would help, low and behold it works fine, been using it for 2 days now without a problem.

So I was reading over at OCUK forums about a guy thats been having trouble with his HD5970 under water and another poster who has a HD5970 said that his card is stable over 35C (I'm assuming under 35C isn't stable) and so thought that I may be experiencing a similar problem

Under water my card idles at ambient temp +3C so because its getting cold its usually at about 22C and playing Call Of Duty Black Ops it reaches 26-28C

With the orginal cooler it idles at about 37C and loads at about 65C

So Can a HD5850 be too cold?

Thanks for your replys