i have a alienware m17x r2 with 2 5870 in crossfire and when i start hwinfo it reads both gpu but after 5-10 seconds the second gpu data is gone but if i game or activate the second gpu the data is back again until i stop gaming then the data is gone again
You probably didn't have ULPS activated before.
This is normal behavior and HWiNFO doesn't force the secondary GPU to be online to preserve power. If GPU-Z reports values while the GPU is sleeping, then it's either forcing it to wake up each cycle, or reports fake values.
You can disable ULPS if you don't like it.