WordPress plugins MISSING (old theme NOT working) Help?

Recently I (accidentally) deleted the theme I was currently using in my ftp client.

I re-uploaded the same theme (sans the few modifications I had made previously) to my ftp client under "/public_html/wordpress/wp-content/themes" like normal, but when I go into my wordpress admin panel, ALL of my plugins are GONE.

And when I activate my theme, nothing shows up but the theme alone. No posts, no nothing. I just get this error message in the sidebar:

"Fatal error: Call to undefined function get_useronline() in /home/meredith/public_html/wordpress/wp-content/themes/Minimalistic/sidebar.php on line 8"

And frankly, I don’t understand what it means.

So I did a restore with a back-up I had downloaded earlier that day, but still nothing is right again.

I tried downloading and uploading my old plugins to my ftp, but when I go to my admin panel, they still don’t show up. I’ve tried uploading them directly to my wordpress admin panel and there’s still nothing.

I just want to know how to fix my old plugins and maybe get my old them back.

Anyone know what I’m doing wrong?

Thanks.