What went wrong was your hard drive is failing. The system cannot find a valid bootable system. You can test this by booting to an external drive (which looks like might have to wait for getting home or to the shop)
If the failure is happening fast - you just had bad luck and it would have failed within days no matter what. Get your stuff off and be glad you got things out before the "house burns to the ground".
If you had a slow failure, then the upgrade could have made things worse. This slow failure can often be made better by zeroing out the whole drive. Bad blocks get marked and for a while, it is reliable. You might buy some months or a year, but it's starting to fail.
Did the technician let you know if she or he felt you had a crisis or a slow issue with the HD?
As an analogy, Imagine a large "house" made of four decks of cards and lots of levels. If the far left hand side is shakey but you only are adding cards to the right, it might stand for a long time. As soon as you touch the left, down it comes.
A system upgrade touches everything - and re-writes the core software needed to boot. Your mac just wasn't up to having critical files written reliably and the upgrade brought those errors to stark light.
Put another way, Lion is running on millions of macs.
Sadly for you, something about your mac was different than most and the results quite painful to your productivity. The good news is many are going through the same pain - discovering how fragile HDD/SSD storage can be when a critical file fails to get written correctly.
I hope you get everything fixed, lose no data and can start enjoying Lion.
Sounds like the partitioning is damaged. If you can boot from OS X on an external drive, use Disk Utility to "Repair Disk". If that reports OK, the Repair the partition with the OS X installation.
The particular kind of Mac might be helpful, and the OS versions.
Also, for Intel Macs, the disk must be partitioned with GUID. If its gotten to be Master Boot Record or Apple Partition, it won't see the disk as a boot source.
Best Answer
Go to System Preferences -> Users and Groups.
On the left sidebar click on your user name and then Login Items.
In that window you can configure which apps to run automatically at startup (click on + and - at the bottom to add or remove apps).
Please note: many of these apps (such as Creative Cloud or Dropbox) have their own switch. Just check their Preferences to activate/deactivate those apps at startup.
For Dropbox, see screenshot attached: as you can see i have the option "Start Dropbox on system startup" unmarked and (as you may expect) it does not run automatically every time i switch my Mac on.