Ok, I've the exact same problem... I've had it about 3 weeks, been working fine, profile switches and everything, then mid game (TF2) it just stopped... Only the right mouse button works, and the dpi switch... Nothing else works. Can't even open the Roccat HUD and click anything as the left mouse button doesnt' work.
Going to try the windows defender thing to see if that works.
Using windows 8.1
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OK, it's not taken long, however as I don't have windows defender, it screwed up any hope of me getting any use out of the mouse, however after trawling through alternate forums, I found that restoring windows to a few days previous was advised. This I did, and upon completion of the windows restoration to 3 days ago (not sure if this is coincidental, but was before a major windows update occured), I opened up the HUD for the ROCCAT Kone XTD and reset the driver once again. HEY PRESTO! IT WORKED! I had full function of my mouse buttons, and the lovely light display reappeared on the mouse.
Luckilly I didn't have to reassign all my profiles, as these were saved and ready to load.
Hope this helps, bit of a computer noob here, but found my way around it, and hope to help some other poor computer noob like me with this very frustrating problem