'Lost' Picasa photos

[GOSMAN]

You will understand my computer illiteracy from the following...  I need help.  

 

 I have several years, hundreds, of photos scattered about my computer including the best 'on' Picasa.  - Always intended to get them organised but I've never been sure how the interplay between My Pictures, Picasa and other photo programs works.  So, I left well alone ...

 

Until yesterday when, experimenting, I hit a 'remove folder from Picasa'  toggle in  an effort to remove a few duplicates.  Disaster!  All my several hundred photos that I considered my 'Picasa' photos all disappeared.

 

Anyone - please tell me I can retrieve them - and how!

 

Thanks.