Yes, during the install there is a point at which the screen blanks as it goes to sleep, this is normal, and I usually just hit the Shift key to wake it up. But that is the only point at which it does it. Once you get the login prompt it doesn't do that.... but if it can't start X, the screen will flicker on and off, as I described above, as it repeatedly tries. You haven't answered my question about the reboot... if it isn't rebooting at that point, just flickering the screen, then it is a problem with X not starting. You need to specifically answer the questions I am asking as accurately as possible otherwise I cannot help you.
If it sounds like what I have described here, then you can determine what is causing X not to start by looking in the /var/log/Xorg.0.log file... but given you are using a 7900 chipset, it is probably that you haven't installed the latest nVidia drivers. Look on the wiki for the article Display Drivers, it has a clear and reliable explanation on how to install these from the GRUB boot menu. Also, have you got an on board graphics chipset as well as a graphics card? Or just onboard, or just card? That is important as I will need to give you instructions if you have more than one chipset.