I'm pretty new to this whole deal. My friend got my started on it today. Essentially my issue is that I'm running 2 4890's and they over heat after running GUIMiner for about 20 minutes. I've ramped up the fan speed to no avail. They still over heat and the system crashes. I'm assuming this isn't normal seeing as how some people run systems 24/7 and successfully make a little money. I've never had any issues with these cards over heating what so ever in any other circumstances. I am running them in CrossFire, but it seems to be the only way to get it to use both cards. If it isn't running in CrossFire, then it will only work at the speed of having just one card running.  Even with just running on one card, it still over heats the card. Any suggestions? I'd really like this deal to pay for a new set of video cards. lol

Thanks for the suggestions. There's a little bit of room between the cards, but they're still a little close for comfort. I did run out of funds on my computer build about 85% of the way through. I got all the major hardware and everything to get it going. At the time I built it, it was quite the power house. A lot of the little details were left out though and frankly other projects came up and things got forgotten. I didn't put a fan on the side of the case, which is right over the cards. However there is a hole there that the fans on the cards themselves can pull air through. I sat down last night before I went to bed and I couldn't remember the last time I cleaned the system out. That in itself is bad as we all know heat kills everything and dust only helps heat. I don't have my air compressor up and running, so I'm going to see if I have a can of air floating around to clean the whole system. I am sort of leery about leaving the side off my case because my son will be all over my computer and more than likely so will the dog. I've got a few other tricks up my sleeve. I'll try a few things out and report back. Hopefully my problems will be solved and my computer will start earning its keep.

also upgrade case you front and rear fans to something [way]more powerful. stock ones was silent enough, but not so mighty and usually have sleeve bearing[silent, but low-resource type]. something branded Noctua, Noise Killer, Cooler Master, Zalman and etc.

newbs giving newbs advice... oh the ironing!

I'm assuming that the 4890's are a similar build to the 4870s.  I just replaced my 4870 yesterday w\ a 6870 and the cooling of the 6870 is FAR SUPERIOR...

With the 4870 I was using the ATI Catalyst overdrive program to manually set the fan speed and monitor the temperature and gpu usage.  Using flags like -v -w128 -f128 I was able to get it to process around 75% and thereby avoid overheating.  Outside of better cooling on the card, I'm not sure what else I could suggest.