A few days ago, my G5 (DP 2ghz PCI-X 1st version; 10.4.9) crashed/froze while in Safari. Restarting after forced shutdown (holding in power button), it hung past the blue screen that usually appears between the grey screen with logo; and the blue screen with startup progress bar. I then tried: 1. Zapping PRAM. Same blue screen hang. 2. Using option key on startup, trying to start up with 2nd internal drive with a fairly fresh (unused) Tiger installed. Same blue screen hang. 2a. Starting up from the Diskwarrior CD (no problems starting up) it reported the discs OK and mounted. Didn't solve the problem. 3. Starting up with Tiger install DVD (no problems starting up) and running disc utility/repair disc, permissions on both internal discs. Same blue screen hang. 4. Disconnecting everything except Apple mouse and keyboard, and removing PCI cards. Removing RAM (3 pairs of 512MB) and trying to start with one pair at a time. Same blue screen hang. 5. Removing internal drives and putting in a new drive. Initialised drive and installed Tiger. No problems until restarting after completing install...then same blue screen hang. 6. Working through everything on the apple support pages about what to do: starting up in safe mode (no problem) and then doing the all the various things (resetting password, permission repair etc); same blue screen on restart. Starting up in single user mode, running fsck and everything else they suggest. Same blue screen hang on reboot. Variations on the blue screen are: Just stays there for hours blank; or the mouse arrow appears then freezes after a minute or so; black screen (no signal) after a second OR a half hour or so. Of course none of what I tried is going to work because it's all aimed at a disc with problems; and I'm having my blue screen of death even with a new disc with a virgin install. I'm working now with my G5 startup disc as the startup disc for my old G4 via enclosure and SATA PCI card (no problems). So what can the cause of my troubles possibly be? -- John Turns out the culprit is the aftermarket video card (X850 XT Apple/ATI video card 256 meg ram). I hadn't suspected it because video seemed to be OK, but when I set out to more thoroughly test the memory, one pair at a time in each of the slot pairs, I first put the OEM video card back in and voila, normal boot. Reinstall the X850: blue screen hang is back.