Hi, so just fitted a brand new 7990 Radeon gpu... But when I use GUIMiner it seems every second the hash value is changin from 70 Mhash to 169 then 490  then to 'connecting...'  this then repeats but with different values...

Also when I log into BTC Guild my average speed is about 490Mhah, half what this card can do.... 

Any ideas