Hello palaste, and welcome to the fedora forum.
What is happening here is that the nvidia drivers supplied by your fedora install are not working well with your video card. What you need to do to fix the problem is to install the proprietary 3D video drivers from Nvidia. There are two ways to go about doing that.
1) The harder way: Download the driver for you card directly from Nvidia's website. They will be compiled against your current kernel version, plus you'll need a few other packages prior to attempting that process.
2) The easier way: Install the Livna repository, then yum install the pre-packaged rpm video driver package from Livna.
To take the easy way (#2), open a command line terminal and type:
rpm -ivh http://rpm.livna.org/livna-release-8.rpm
rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-livna
yum install kmod-nvidia
Then reboot. There are many current threads regarding issues of installing Nvidia video drivers on F8 as well a numerous how-to guides. Use the search function to review some of those threads. I don't know if the 8600GT card is affected, but the 8800 series of cards are having problems with the current livna kmod-nvidia package in F8 and the drivers from the livna-testing repo seem to be fixing this issue, for some.