Stuck iMac during 10.6.2 to 10.6.8 OS combo update

Dear community,

I recently had to wipe out an iMac HDD and reinstall the OS. The install DVD contained OS X Snow Leopard 10.6.2, and I wished to upgrade to Mavericks (10.9) by doing an intermediate update to 10.6.8, as required by the new OS installer.

After a successful disk erase & OS installation from DVD, I tried to update the OS by using the 10.6.8 Combo update http://support.apple.com/kb/dl1399, which was located on an external hard drive. Just before finishing the update, the screen went black and there was no way to recover the system. Fan and internal HDD were both spinning, so the system was stuck for an unknown reason.

After waiting for 15 minutes, I decided to switch off the computer manually with the power button, and since then the iMac won't boot any more. Here's a list of what I tried:

- Boot from cd ("C" during startup): impossible, another disc is currently in the drive, and can't eject it

- Safe mode: won't load in 30 minutes, I guess it won't load at all

- Reset NVRAM: no effect

- Single user mode:

- "fsck -fy": no effect, volume is OK;

- reinstalling the updates from within su mode "softwareupdate -i -a" (hoping to reinstall it and get rid of the possible crap): impossible, there is no network connection.

Any help would be very welcome 🙂