According to the log file in the OP, this looks like it's a problem with the database. You may want to check that the wallet.dat file is intact or if it's a problem with the blockchain download on your computer.
Sadly, the easiest way to do this is a full rescan using the code:
This will validate that all of the indexes you have already downloaded are accurate (but will take as long as the initial installaion - almost).
(Also, to the members that have posted earlier, just run a google search to find what an I/O error is. It is an Input/Output error so could be caused by reading a database -which in this case it probably is).
If the resync doesn't work, if you have a backup of the wallet.dat file you will need that to try to recover the wallet and get it functioning again (you may actually want to do this first, renaming the original wallet.dat file to wallet.dat.1 before you insert the wallet.dat file into that directly - do not delete until you know the next file works as the next file could also be corrupted).