Troubleshooting MySQL Wordpress

In the process of trying to install iDevAffiliate and creating a new database, I messed up my existing WordPress database. I'm not even sure what I did, but I'm now getting some WordPress errors that point to database problems.

One error is that the Membermouse plugin reports: "Currently MemberMouse can't utilize the cache." A related problem is that when I attempt to update a plugin, Wordpress now takes me to a page that says "To perform the requested action, WordPress needs to access your web server. Please enter your FTP credentials to proceed. If you do not remember your credentials, you should contact your web host." Finally, when I attempt to upload an image to the media library, I get this message: "The uploaded file could not be moved to wp-content/uploads/2014/11." I have no idea why it's trying to move it to 2014/11 when it should be uploading to 2015/01.

At first, I thought these were problems with the directory permissions, which I had also changed while trying to create the idevaffiliate directory in the same directory as wp-content, wp-admin, etc. But the directories are all set to 755 now, and that didn't make any difference.

So how do I do basic trouble-shooting steps with MySQL and WordPress? I'm running a LEMP stack on Amazon EC2, so I Putty in and would love to get the Linux commands to do such things as check to see that the database credentials in wp-config.php is still allowing access to the database, or what else might be wrong.

I'll owe you a free membership at CoolHotNot.com (and more) if you help me fix this! Thanks.