Debian WHEEZY does not boot after it was successfully installed. I had to install it once again in an Expert mode and explicitly check "Install GRUB to MBR" option. Then the system booted fine.
I'm afraid that it is a side-effect of a FIX of another bug, which I faced several weeks ago. Then the system installed from USB key could boot only using the installation key (GRUB installed on the key instead of an internal disk) There was recommended to disable the "install GRUB to MBR" option.