The best way to do this is to follow these instructions
1) after logging into FTP for your site rename the plugins directory to plugins.hold

2) Load the WP-Admin and go to plugins. (Note: It will say that you dont have any plugins installed and that files are missing. This is okay)

3) Go back to your FTP and rename the folder back to just plugins.

4) Reactivate all the plugins except for the two that caused the problem. Then activate only one of those two plugins and see if it is the one that caused the problem. If it is the one that caused the problem repeat the entire process but activate the other plugin this time. If the first one you activated of the two worked then try activating the second one to see if the problem comes back, if it does then you know that plugin either has bad code or code that conflicts with another plugin you are using.

Hope that helps and is not too confusing.