Activate Plugins when Dashboard down

Hi,

Is there a way to reactivate plugins without access to the dashboard.

My website is run OK, but the login has started throwing a “Call to undefined method” error. In trying to track down the issue I was going to rule out it being plug-in related by deactivating them by renaming the plugin folder via ftp. If it proves not to be a plug-in issue then I will still not have access to the dashboard, and so will not be able to reactive them. Which means much of the functionality of my running site could be compromised.

Any ideas of what to try.

Thanks