Why does my iMac shut down before it can boot up After installing 7.3 update on my iMac?

Question

After installing 7.3 last night, I hit restart and went to bed.  My intel iMac i7 3.4ghz was powered down this morning, and only after unplugging,waiting, rep plugging,
It finally powered on, only to boot to the gray apple screen, go black and silent.  (this exact issue had me lugging it back to apple a month after purchase, today is 93 days)
Recovery mode got me about one second further in bottling up before shutting off.
I was forced to upgrade  from an unproblematic pc g5, after iCloud, so do not own snow leopard and was told I would never need a re install disc. 
Has anyone having the powering off during boot after updating to 7.3?

Answer 1

omg. I would copy and paste your original post to the iMac section. You're talking about a fine piece of equipment, the Intel iMac i7 3.4ghz , and you should not be having such problems. Maybe others in the iMac i7 community might also have some ideas.
Re: the safe boot. That's good that it worked. This is fairly new and very, very helpful with a dead computer because at least you can get to Safari, get to the Internet and get ideas and seek help.
But why did it shut off after a while? That's not right. No reason it should have done that.
From something you said I would worry about your power supply problem or this PerIphrEa. I don't know what that is but Migration is built into Lion OS, no? Third party perificials (or apps) can certainly cause conflicts and not work as well as advertised.
Also, seriously, I would get some tape, like duct tape, and tape up that loose power supply.
Why do you need something extra for your migration? (Or is the reason your old PowerPC G5 needs to run Lion but it can't?).
If that is the problem, here's an idea. Continue the canibalization of your PowerPC G5, take out it's hard drive(s). Buy an 'enclosure' to put the hard drive in and allow you to connect this hard drive to your new machine, the beautiful iMac i7, using the old hard drive as an external drive.
I did exactly this with my old PowerPC G5, using this enclosure, a Macally G-S350SUA, info at: http://www.macally.com/en/product/ipod4show.asp?ArticleID=215
I now use this for my Time Machine backups.
Re:What is the proper amount of time the computer needs to be unplugged? This would worry me. I turn off my comuter NOT by unplugging it but by holding the power on button for about 3-4 seconds and then it turns off.
I then wait 5 long seconds before pressing the power on button again to turn the computer back on.
Having to plug in and unplug and plug in and having to wait ten minutes for it to work is not normal.
Is there a power supply issue in your home, perhaps?
Considering the value of this machine and the fact that it may still be under warrenty, I'd consider the  weeklong diagnostic. Would the machine have the same need to wait ten minutes to turn on at the Apple place?
What if you plug it in at a friend's house, or an office or library? Would it still take ten minutes before you could turn the machine on?
It might seem horrible to have to wait a week...or to do this again and again but I'd recommend taking full advantage of your warrenty, keep sticking this problem back to Apple and insist it gets made right. It will be worth it in the long run.