won't boot from selected drive after power outage

I have a 3.2 GHz Quad-Core Intel Xeon desktop running 10.8.5. The startup disk is an SSD disk. We had a momentary power outage, and when I re-started the computer I got the "prohibitory" or "no entry" sign (circle with slash) for a second, then the apple--I have an identical system on a regular HD, and it started up with that.

I've tried starting with command-option PR, shift, option (it sees the SSD drive, but even if I select it it goes to the other HD). I've repaired permissions. I've "verified" the SSD disk using disk utility--it says everything is OK. I've tried opening some files on the SSD drive, and they open fine.

The issue for me is that I had a lot of stuff just on the desktop, and unless I start from the SSD the SSD desktop files don't appear--maybe they're hiding somewhere, but I don't know where. Also all the bookmarks in Safari have disappeared, etc.

And yes, the SSD is selected as the startup disk in system preferences. It just doesn't seem to want to start up from there.

We have had other power outages before, but this is a new problem. I've read a lot online, but haven't seen this exact problem.

If no solution can be found. It is always possible that with a power outage there could have also been a power surge. And a power surge can damage electronics. Thus your Mac Pro's SSD could have sustained damage.

Just something to consider.

- Nick

We have had other power outages before, but this is a new problem. I've read a lot online, but haven't seen this exact problem.

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Like Nick said, the SSD could have sustained damage during the power outage - surge. You need to consider buying a good UPS to avoid that in the future.

Do you have a USB/flash drive with installer so you can reinstall OS X? It doesn't overwrite user files.
Oh, you didn't mention - did you start up in Recovery partition to try reinstalling? Read here:
https://support.apple.com/en-us/HT201314

Or, do you have a Time Machine backup to restore from?
https://support.apple.com/en-us/HT201250

Thanks for the suggestions. I ended up re-installing the system on the SSD from the Internet--it worked.