"Arduino UNO" recognized in device drivers but invisible in IDE

Hi everyone..
My arduino was working perfectly a few weeks ago but since then, I hadn't used it. I plugged it in to the PC today but it doesn't work properly.
In the device manger there is an entry for "Arduino UNO" on Port 13 but there is also a small yellow exclamation mark next to the icon. (I'm on windows XP).

port 13 doesn't show up in the IDE either..
What should I do?

I just found this message in the "properties" dialog of the device manager.
"Windows cannot start this hardware device because its configuration information (in the registry) is incomplete or damaged. (Code 19)"

...googling now. :wink: but please post your suggestions.

ok.. just reinstalled the drivers and everything seems to work.

I had the same problem with my windows 7 machine, it won't work no matter how many times I uninstall/reinstall the driver.