Created a bootable drive but for some unknown reason I can't boot into it, screen goes no signal detected then stays blank, I did leave it like that for over an hour before switching off. Flash drives stays active (Light on) I have tried 3 flash drives which were all new! I have recently changed my GPU to a NVIDIA GeForce GTX 780 3072 MB which has been flashed. Any help would be appreciated. I am currently running El Capitan 5,1 Mac Pro mid 2010
Mac Pro
The SanDisk USB sticks do seem to work better than many out there. So many people use the cheapest ones out there which I why I made the comment.
I'll have to leave any GPU issues to @Grant since I've never used a flashed GPU in a MacPro so I am not familiar with which ones will work best.
The fact that the USB stick has its LED lit for so long is a concern. Have you tried other USB ports?
You can also remove the side cover & clear shield to check the LEDs on the Logic Board. I believe some of the diagnostic LEDs are located near the memory slots, but I think there may be other LEDs elsewhere on the Logic Board. Mark down which LEDs are lit and which are dark and post the information here. You may be able to find references to those diagnostics LEDs online.
You may want to try boot a Linux USB drive as it may provide some clues about the hardware. Normally I would suggest using Knoppix, but Knoppix doesn't display anything on the Mac's screen until late into the boot process which won't help you here. Instead try creating a bootable Ubuntu or Linux Mint USB drive. If you use a Live USB version, then you will need to press either "Esc" or "Shift" while Linux is booting in order to view the boot log as the system boots. If the boot stalls out maybe the log will give you a clue. You will need to Option Boot the Linux USB drive and select the orange icon labeled "EFI".
Could you try booting up with the old graphics card to see whether the new boot drive or something else is the problem?
and what version of MacOS did you install onto that drive, so that you can boot from it?
and what method did you use to place the version there?
Did you use a different brand of USB stick? Macs can be very picky about the USB sticks used for booting. Plus the quality of many USB sticks is extremely poor.
what version are you trying to install?
I'm trying to boot into my flash drive? .... just to make sure it works.
I used a SanDisk not the cheapest out there, I have had them for a while and have booted from these drives in the past without a hitch
I installed El Capitan, I formatted the it as Journalled with GUID partition couldn't see any other option if I'm honest but may have missed it, done this before (booting from flash drive) and never had an issue just thought you guys would say it was something to do with the GPU
Hi there thanks for such a detailed reply unfortunately I don't understand much about what you are saying here I am more involved with software (Music) and all this is new to me as I had a partner who sorted out all this for me who's sadly (Very) no longer with us, after watching a few YT vids I can't understand why I'm having this problem as no one else is reporting a problem, I eventually want to install Catalina but I'm reading some horror stories so though I would take it one step at a time.
Unable to boot from flash drive...
