Mac pro won't boot :(

A blackout could fry any number of components in your mac. This is why a UPS (uninterruptible power supply) is generally recommended. It is essentially a battery between your mac and the wall outlet and gives you time to shut the machine down in the event of a blackout.

Try reseting The PRAM by following this article
http://support.apple.com/kb/ht1379

If that doesn't work, my first suggestion is to boot from a backup, assuming you have one. If you don't, that's your first mistake! See if the machine will boot to a separate drive. If it does, then you're hard drive is fried, which is the most likely problem.

If you don't have a backup, remove you original HD, install a different one that you can wipe. Boot from the install disc (hold "c" when booting to boot from DVD) and install a fresh copy of OS X on this drive. Boot up form this new install and see if it works. Again, if this works, it's your HD.

If this doesn't work, put in the install disc and boot up holding "D". This will enter the "Apple Hardware Test". Choose "extended testing" and run the test, which can take a while. This should show if there are any hardware problems with your computer. If it shows up something, get in contact with Applecare. If nothing shows up, I'd still contact Applecare and get them to look at it.
Even though they will run their own tests on it, the benefit of doing the test yourself is that you can provide them with the error code (take note of any that come up after the test) which will help them in fixing it.

Regards