strange problem here.
Mac pro 2008, 8 core.
If i want to boot (computer was off) i get the grey screen problem (hangs).
I do a PRAM reset >> it boots to another 10.6.8 ( have 3 HD's with 10.6.8, 10.7.4 and 10.7.5).
then i choose 10.7.5 as boot-volume (system preferences) >> 10.7.5 boots normally.
If I do ea reboot (apple-menu) it reboots fine into 10.7.5.
If i shut down the computer >> start the computer again >> grey screen-hanging...
all other system running fine, also boot fine after a complete shutdown, only 10.7.5 behaves strange...
all voodoo (diskpermissions, hardwaretest, HD recovery) done, doesn't help.
Any help welcome.
Try this on the 10.7.5 drive. No logical explanation for what you are seeing though.
Startup Grey Screen
Retrieving data ...