Help! Won't let me open, says. "another app already has open"...

Hello!

I have been using LR for about a year, I use it daily. I edited some of a session last night, then went to bed. When I woke up this morning and turned on the computer, my last 2 weeks of folders of sessions was gone. Then to make things worse, I restarted and shut down my computer again to see if they would magically reappear and now every time I try to open the catalog with dozens of my recent pictures/folders/sessions in I get this message: "The Lightroom Catalog named "rename" cannot be opened because another app already has it open. Quit the other copy of LR before trying to reload." But I didn't have LR open on any other device, and I don't understand how it could be open in another app and if so where to go to close it...I only have LR on this computer. I can get into lightroom and upload pictures but only because I created a new catalog. I cannot get into the catalog I need desparately to. I already tried resetting my computer to an earlier date which didn't help. Thank you!!!!