Why might extracted Snow Leopard MacBookPro drive no longer boot under IMAC Lion?

Question

I'm hoping someone can give a  likely explanation for the following sequence of events, and also recommend some next steps.  I've been backing up, using Time Machine on a partitioned drive, my 2008 IMAC with Lion and my 2008 MacBookPro with Snow Leopard.  Being out of town for the last 3 months, MBP backups were not possible and Murphy's law kicked in as the MBP refused to boot, no chime and black screen.  Tried all the discussion group suggestions and then returned home to visit the Apple store.
1. Apple store said it was my logic board and repair would be $310, but if the hard drive was a problem Apple Repair would just swap it out.  Apple store would do backup of the drive before sending it for repair if I provided an empty drive.
2.  As I didn't have a spare drive, I  purchased an OWC USB 3.0 enclosure kit  and inserted the drive from the MBP.
3.  Plugging into the running IMAC, it came up and everything looked good.  TIme Machine recognize the new drive and included it in its list of devices to NOT backup.
4.  I decided to see if I could boot the IMAC from this MBP drive by doing a restart with the option key held.  It gave me the choice and it worked.  Everything looked good and I was able to update my mail and to print.  I decided to have Time Machine do a backup and included the IMAC internal drive in the list of devices NOT to backup.  Time Machine warned that this MBP was a new computer and that i'd not be able to go back, which concerned me as the whole purpose is to be able to move to a new system if necessary.  I did a backup anyway and it copied about 25 GB of some 158 GB so it must have been an update.  Everything looked good.
5.  I then did a restart and came up under Lion.  However the MBP drive was no longer visible on the desktop, but the system recognized that the OWC MBP drive was USB connected.  This was a concern.
6.  I did a shut down of the IMAC and removed the MBP drive.  Rebooted IMAC and then inserted USB MBP drive.  It came up this time. Its contents looked good.
7.  I then did a restart with the option key held.  It gave me the choice to boot from the MBP drive as before and I took it.  However it hung with a gray screen, circle with slash, and spinning wheel.  No activity from the MBP so I forced IMAC shutdown and removed the MBP drive.
8.   Booted the IMAC, but can not get the MBP drive to appear on the desktop although it is recognized as a USB device.  No activity from the MBP drive as indicated by no flashing of its light.
I'm mystified as to what has happened.  Have I corrupted the MBP drive, or is it likely a hardware failure?  I'm thinking about a new computer, but was staying with Snow Leopard as it was only way to keep my scanner working.  It was momentarily convenient to be able to boot into Snow Leopard and to work as usual.  What can I do with my TIme Machine backup of the MBP if the MBP drive is corrupted?  Any help here would be greatly appreciated.

Answer 1

Thanks Pete, but it doesn't solve my problem.
Apple does something to the recovery partition to make it invisible. When I was trying to setup my 16GB USB stick drive as a "Recoverable Partition", since I don't have one on my main Lion drive, it made it invisible also. But during the process it failed to finish but has left my USB drive invisible under Lion and nothing that I've tried has been able to undue that. (See Above). What is it that I need to do to get my USB Flash drive visible again under Lion. It is visible under Snow Leopard and it is visible under the lion install utitlties (I made a installer DVD from original internet downloaded Lion installer) but not under disk utilities on lion or the lion desktop! I've reformated under both the above(Snow Leopard & Installer utilities) were I had access to the USB Drive but that didn't undue whatever Apple does to make the recovery partition and my USB Drive invisible because once I boot back into Lion, it's still not there! So the $64,000 question is how do I get my USB Flash drive visible again under Lion?
Hope this help you to understand my situration.
Ian