Chosen Solution
My MacPro tower does not light up the screen after startup. The chime goes off, but nothing happens! I have tried holding the P and R and COMMAND keys down on startup, but that made no difference! It has Yosemite10.10 installed, but if I can get it going I want to install SNOW LEOPARD on it as Yosemite seems to have too many bugs in it yet. Anybody has any good advice for me?
Boot to original or Snow Leopard install disks (or other volume). This system can run the last version of OS X 10.7 “Lion” if upgraded to at least 2 GB of RAM. Although it has a 64-bit processor, it has a 32-bit EFI and cannot boot in 64-bit mode. It also does not support “OpenCL” running the default video card or the other build-to-order video cards that were offered via custom configuration. If this answer is acceptable please remember to return and mark it accepted.
Good to hear you got it fixed. As for resetting the PRAM, one should press and hold Option-Command-P-R right after the startup chime.
Try to boot using option key on an priginal apple,keyboard. If,there,os a working graphics card you will see the choices,for any startup disk. I,for example,have a newer card in a 2008 Mac Pro which glitches on startup as those card,is only sort of supported,but using the option key allows,it to,work,fine once I choose the appropriate startup disk. It,should not be this way of course but this works.for me. It does sound as if your graphics card is not installed or os defective,or cables are inappropriate. There are two outputs so try the other alternative outputs.
