Can't get into dashboard after installing plugins

I have limited experience with plugins. I try to stick to user friendly ones that just install and are easily placed into pages. Please keep in mind my beginner status when commenting. THANK YOU!!!

I installed a couple of event registering plugins and it somehow made my homepage slider disappear.

I’d like to just get rid of the plugins all together but this notification pops up every time I log into the admin:

Strict Standards: Static function RangePlugin::getInstance() should not be abstract in /home/drjoel/sequoiamedicine.com/wp-content/plugins/twitter-widget-pro/range-plugin-framework.php on line 157

Please help!