Mac Pro 1,1 won't boot up after update to 10.10.5.

Hi guys,
I made a huge mistake to update my Yosemite to 10.10.5 and after it rebooted, nothing worked! Now I get no display, no start-up chime, only the power solid light on and the cooling fun. Can't even start in safe mode, because the keyboard does not respond. Any help will be appreciated.
Thanks.