Oh the joys of usb wifi on linux!
Whilst I can't give you an exact answer to your problem (there are many), i have been through a similar process trying to get a cisco/linksys usb device to work. you'd think such big names would be better supported, but alas, not.
I know it's a silly question, but someone has to ask it.... There is often a little "wifi on/off" switch on laptops these days... just double-check that it's in the "on" position. To my shame I have to admit to spending several hours trying to fix my own wifi, only to have my g/f point out "it's little light isnt on, maybe it needs a new light"....
After that, which version of Kubuntu are you using? There was an outstanding bug in ubuntu (and by extension in Kubuntu, Xubuntu EDubuntu etc etc) with regard to the system loading multiple modules for some usb wifi devices.
i see that you used lsmod to check the device driver was loading correctly (yay!), can you use lsmod to check if the module “rt2800usb” is loading? if it is, that's probably the problem. (there are lots of posts on launchpad about this, with the ultimate answer being here: https://answers.launchpad.net/ubuntu...question/87970
I suspect it will be there, since all the information you have provided pretty much matches exactly with the various posts about this chipset (see also here: https://bugs.launchpad.net/ubuntu/+s...ux/+bug/460323
long story short, if this is your problem, take the following steps to fix it.
1. as root, edit the file "/etc/modprobe.d/blacklist.conf" and add the line "blacklist rt2800usb" to the end of the file.
2. turn your computer off and back on again. (shutdown and reboot, don't just yank the cord out!)
If this makes it work, yay!
if it breaks it more, just remove the line "blacklist rt2800usb" from "/etc/modprobe.d/blacklist.conf" and it will go back to how it is now.