12.04 boot hangs when cold; restart OK, boot within 5 minutes OK

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http://askubuntu.com – I had many years of reliable behavior with my desktop using 10.04 LTS. After upgrading to 12.04 LTS, my desktop is now acting very strange with booting. Rebooting using the "restart" option always works without any problem. Booting after a normal "shutdown" within about 5-10 minutes works without any problem. But booting after a normal "shutdown" with the computer inactive for a long time results in a hang before grub, before even the manufacturer's splash screen. I'm not sure exactly the time period required for this to happen, but I normally shut down the computer overnight. Most of th (HowTos)