Haven't you been having trouble with this for a while? It's little hard to advise w/o reviewing what you have tried so far, but here are some basic suggestions. I got 5x5850 going on BAMT, but it was pretty unstable at first. You have probably already tried this, but if you have made *any* hardware configuration changes, even if they seem trivial, boot from a fresh copy of BAMT. At one point I swapped one 5850 for another, so the two were in different slots, and BAMT completely freaked out about this. I had to start over with a fresh copy. Also, you might try being uber anal about that fresh copy, as in write zeros to the usb drive to completely wipe it and then use dd in linux as opposed to win32diskimager to copy the image. Another thing to try is to get the cards going manually in phoenix - i.e. cd /opt/miners/phoenix - and start each card manually. If you can get all 5 going this way, this will at least tell you that the problem is specific to the process of starting automatically from the configuration script. Also, try starting your GPUs with *REALLY* moderate settings (like 600/500 core/clock at stock voltage). If they work this way, you know you are pushing the clocks of one or more GPUs too much. If they still don't work, lower the voltage - then if they work you know your PSU can't handle 5 cards at stock voltage.
I think BAMT is awesome, but for me it did a lot of really strange things. I know it's supposed to be essentially plug and play, but in my experience it was a bit less friendly than this. I've switched now to cgminer on a flavor of ubuntu 11.04 (Peppermint Two), and I'm liking this better. I definitely recommend cgminer if you can't get BAMT working.
thanks for your suggestion,I will try