This is do because the rfkill tends to shutdown the radio off of the chipset rtl8187 which I believe the alpha has. This has been discussed so many times and was put in the wiki of backtrack. Rtl8187 vs r8187 - BackTrack Linux here. You have to kick the wifi off of the hard block of the rfkill. You could try the "rfkill list" to see for your self which it should say yes on hard block and once you go to the website and you do the commands then it should say no.