For the four days I've had Cubase SX, I've been trying to bust my tail to power through the learning curve as quickly as possible. I made it through all the “Getting Started” tutorials in one day, but my progress has been greatly slowed by Windows not detecting my stupid dongle key. It's really tough to use Cubase SX when you can't get the software to load.
I asked around on the Cubase.net forums, but I wasn't finding any solutions to my problems. I did some further investigating on the Steinberg.net support site. I found a page that included all sorts of details. http://knowledgebase.steinberg.de/96_1.html
It turns out that keys with a serial number (found on the USB key itself) starting with less than 5 do not work with motherboards using the nVidia nForce 3 chipset. The problem was corrected in newer USB keys that use 5 as the first number. You can read all about it in the link above.
It turns out link suggest using a USB hub. Well, I didn't have a USB hub, but I did have an extra USB 2.0 / Firewire PCI card laying around. So I tossed it into a free PCI slot (hopefully I won't have any IRQ issues). I plugged in the key and it was immediately detected like it is supposed to. AWESOME!
I was really afraid that I was gonna have to ship back my copy of Cubase SX3 to my disributor and wait for them to send me a new one. That would have put me in ULTRA PISSED mode. Luckily, I found a solution that cost me less than shipping on a new box. (You can knab these USB 2.0 / Firewire PCI cards for about $5 usually on newegg.com).