This is very unlikely - I've never seen a plugin designed to do this.. it would be plain dangerous (and pointless) for a plugin to do.

Instead, it's most likely that you've got some plugin conflict, or perhaps the plugin now requires a newer version of wordpress than what you're using.. or perhaps two plugins are conflicting with each other.

First step, is to try to figure out which plugin is causing the problem...

Edit your wp-config.php file to set the debug flag to true...
change:
define('WP_DEBUG', false);
to:
define('WP_DEBUG', true);

Then refresh your browser and see what it says - you should have some error text displayed which will hopefully point you at the plugin which is failing.

You can then temporarily disable that plugin by moving it's folder out of your plugins directory (eg. /.../mysite.com/wp-content/plugins/badplugin) to somewhere else.

Once the offending plugin has been moved, you should be able to log in again - you can always move all plugins out of that directory if you need to get get in quickly

Once you've updated wordpress.. you can try moving the plugin back in - hopefully it'll do the trick, otherwise.. you may need to contact the plugin vendor.

EDIT: remember to change the debug flag back to false when you're done too!

Cheers,
Michael