Did you make a backup of your wallet.dat file? If so you may be able to reinstall the client and then replace the wallet.dat with the backup, you should then be able to access your coins. If not, make a backup now - I'm not sure, but hopefully the original will have remained unchanged when you updated... to make a backup, find the location of the wallet.dat file: https://en.bitcoin.it/wiki/Data_directory and copy it to a safe place