Inspiron N5010: internal Wi-Fi works, no external (USB) Wi-Fi will work

I have a Dell Inspiron N5010 (15R), bought 12/2010. Running Windows 7 Home Premium 64-bit. Built-in Wi-Fi adapter works fine, but I can't get ANY external (USB) Wi-Fi adapter to work. First tried a Blueproton GSky adapter; system said "bad USB device", I think. Worked on my old laptop (Inspiron 1100 running Windows XP, until it was stolen), but I thought "okay, maybe GSky happened to die recently". But now I just bought a Rosewill model RNX-N2LX adapter, and it ALSO doesn't work.  Device just flashes its LED forever; config utility launches and immediately exits, again and again forever; in Device Manager it says device and driver are fine. I tried quitting the Rosewill config utility launcher (tray icon), and enabling Wireless Zero Configuration, but it just says no connections available.  And Troubleshooter isn't able to fix it, and says maybe there is something wrong with the device. Tried disabling my firewall (ZoneAlarm); no difference. Other USB devices (camera, external disk drive) work fine in same USB ports. Is there something about the Dell Inspiron N5010 that is "allergic" to external Wi-Fi adapters ?  I have tried them with built-in Wi-Fi adapter (DW1510) enabled and disabled; no difference.  Or maybe none of these devices have 64-bit drivers ?  Shouldn't I get some kind of error message if that were the case ?  Do I need to install in Compatibility Mode, whatever that is ?  Rosewill adapter uses Realtek 8192SU chipset; GSky uses RealTek 8187L chipset.  I would assume these chipsets are so popular that 64-bit drivers would be available. Help !