2.3 > 2.5 Problems! PLEASE HELP ME!!

OK, so I upgraded to 2.5, but I didn’t like the Dashboard and the inability to find my plug-ins. So, I decided to go ahead and move back to 2.3. I followed the backup instructions of putting my ‘www’ folder on my computer.

I put the 2.3 www folder back onto my FTP, and now it isn’t working right.

I can see my blog when I go to the site, but when I try to go to the wp-admin I get the following message:

Warning: Cannot modify header information – headers already sent by (output started at /home/o*******/public_html/wp-config.php:47) in /home/o*******/public_html/wp-includes/pluggable.php on line 390

(the o******* is protecting my login name, as I am not sure how safe it is to share it)

Please tell me how I can fix this!

Thank you in advance for your help.
Jason