I don't know if this will help, but consider these questions:
(1) You have a 3.10-7 slh kernel, but that is for aptosid users, and here you are on the siduction forum, and the most recent towo kernel for siduction users is 3.10-4 (and perhaps there are reasons for this ....). So, can you use
kernel-remover
and remove the 3.10-7er and boot your previous kernel version?
(2)
This installation did not work and I found out, that I should use the nouveau-driver.
Why -- is there a source for this guidance? If you need the dual monitor function of the nvidia driver, and if the nvidia driver (for some reason) isn't supported with the 3.10-7 kernel, then here is another reason to consider removing 3.10-7 and going back to the earlier kernel.
Also, if it is the case that the nvidia driver is not supported by 3.10-7, how do you know nouveau is supported?
In the last 24 hours, I have seen xserver-xorg updates, so there is another possible source of problems or compatibility issues.
Here my system is fully updated KDE 4.11, with nvidia proprietary driver, and kernel 3.10-4.towo-siduction-amd64 and everything is working correctly.